The dynamic dma kmalloc creation can run into trouble if a
GFP_ATOMIC allocation is the first one performed for a certain size
of dma kmalloc slab.
- Move the adding of the slab to sysfs into a workqueue
(sysfs does GFP_KERNEL allocations)
- Do not call kmem_cache_destroy() (uses slub_lock)
- Only acquire the slub_lock once and--if we cannot wait--do a trylock.
This introduces a slight risk of the first kmalloc(x, GFP_DMA|GFP_ATOMIC)
for a range of sizes failing due to another process holding the slub_lock.
However, we only need to acquire the spinlock once in order to establish
each power of two DMA kmalloc cache. The possible conflict is with the
slub_lock taken during slab management actions (create / remove slab cache).
It is rather typical that a driver will first fill its buffers using
GFP_KERNEL allocations which will wait until the slub_lock can be acquired.
Drivers will also create its slab caches first outside of an atomic
context before starting to use atomic kmalloc from an interrupt context.
If there are any failures then they will occur early after boot or when
loading of multiple drivers concurrently. Drivers can already accomodate
failures of GFP_ATOMIC for other reasons. Retries will then create the slab.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
The MAX_PARTIAL checks were supposed to be an optimization. However, slab
shrinking is a manually triggered process either through running slabinfo
or by the kernel calling kmem_cache_shrink.
If one really wants to shrink a slab then all operations should be done
regardless of the size of the partial list. This also fixes an issue that
could surface if the number of partial slabs was initially above MAX_PARTIAL
in kmem_cache_shrink and later drops below MAX_PARTIAL through the
elimination of empty slabs on the partial list (rare). In that case a few
slabs may be left off the partial list (and only be put back when they
are empty).
Signed-off-by: Christoph Lameter <clameter@sgi.com>
We ClearSlabDebug() before the last SlabDebug() check. Clear it later.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Ingo noticed that the SLUB code does include the lock debugging free
check.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Slab destructors were no longer supported after Christoph's
c59def9f22 change. They've been
BUGs for both slab and slub, and slob never supported them
either.
This rips out support for the dtor pointer from kmem_cache_create()
completely and fixes up every single callsite in the kernel (there were
about 224, not including the slab allocator definitions themselves,
or the documentation references).
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
The slab and slob allocators already did this right, but slub would call
"get_object_page()" on the magic ZERO_SIZE_PTR, with all kinds of nasty
end results.
Noted by Ingo Molnar.
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We currently cannot disable CONFIG_SLUB_DEBUG for CONFIG_NUMA. Now that
embedded systems start to use NUMA we may need this.
Put an #ifdef around places where NUMA only code uses fields only valid
for CONFIG_SLUB_DEBUG.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Sysfs can do a gazillion things when called. Make sure that we do not call
any sysfs functions while holding the slub_lock.
Just protect the essentials:
1. The list of all slab caches
2. The kmalloc_dma array
3. The ref counters of the slabs.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The objects per slab increase with the current patches in mm since we allow up
to order 3 allocs by default. More patches in mm actually allow to use 2M or
higher sized slabs. For slab validation we need per object bitmaps in order
to check a slab. We end up with up to 64k objects per slab resulting in a
potential requirement of 8K stack space. That does not look good.
Allocate the bit arrays via kmalloc.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
It becomes now easy to support the zeroing allocs with generic inline
functions in slab.h. Provide inline definitions to allow the continued use of
kzalloc, kmem_cache_zalloc etc but remove other definitions of zeroing
functions from the slab allocators and util.c.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We can get to the length of the object through the kmem_cache_structure. The
additional parameter does no good and causes the compiler to generate bad
code.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Do proper spacing and we only need to do this in steps of 8.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
There is no need to caculate the dma slab size ourselves. We can simply
lookup the size of the corresponding non dma slab.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kmalloc_index is a long series of comparisons. The attempt to replace
kmalloc_index with something more efficient like ilog2 failed due to compiler
issues with constant folding on gcc 3.3 / powerpc.
kmalloc_index()'es long list of comparisons works fine for constant folding
since all the comparisons are optimized away. However, SLUB also uses
kmalloc_index to determine the slab to use for the __kmalloc_xxx functions.
This leads to a large set of comparisons in get_slab().
The patch here allows to get rid of that list of comparisons in get_slab():
1. If the requested size is larger than 192 then we can simply use
fls to determine the slab index since all larger slabs are
of the power of two type.
2. If the requested size is smaller then we cannot use fls since there
are non power of two caches to be considered. However, the sizes are
in a managable range. So we divide the size by 8. Then we have only
24 possibilities left and then we simply look up the kmalloc index
in a table.
Code size of slub.o decreases by more than 200 bytes through this patch.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We modify the kmalloc_cache_dma[] array without proper locking. Do the proper
locking and undo the dma cache creation if another processor has already
created it.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The rarely used dma functionality in get_slab() makes the function too
complex. The compiler begins to spill variables from the working set onto the
stack. The created function is only used in extremely rare cases so make sure
that the compiler does not decide on its own to merge it back into get_slab().
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add #ifdefs around data structures only needed if debugging is compiled into
SLUB.
Add inlines to small functions to reduce code size.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
A kernel convention for many allocators is that if __GFP_ZERO is passed to an
allocator then the allocated memory should be zeroed.
This is currently not supported by the slab allocators. The inconsistency
makes it difficult to implement in derived allocators such as in the uncached
allocator and the pool allocators.
In addition the support zeroed allocations in the slab allocators does not
have a consistent API. There are no zeroing allocator functions for NUMA node
placement (kmalloc_node, kmem_cache_alloc_node). The zeroing allocations are
only provided for default allocs (kzalloc, kmem_cache_zalloc_node).
__GFP_ZERO will make zeroing universally available and does not require any
addititional functions.
So add the necessary logic to all slab allocators to support __GFP_ZERO.
The code is added to the hot path. The gfp flags are on the stack and so the
cacheline is readily available for checking if we want a zeroed object.
Zeroing while allocating is now a frequent operation and we seem to be
gradually approaching a 1-1 parity between zeroing and not zeroing allocs.
The current tree has 3476 uses of kmalloc vs 2731 uses of kzalloc.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Define ZERO_OR_NULL_PTR macro to be able to remove the checks from the
allocators. Move ZERO_SIZE_PTR related stuff into slab.h.
Make ZERO_SIZE_PTR work for all slab allocators and get rid of the
WARN_ON_ONCE(size == 0) that is still remaining in SLAB.
Make slub return NULL like the other allocators if a too large memory segment
is requested via __kmalloc.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The size of a kmalloc object is readily available via ksize(). ksize is
provided by all allocators and thus we can implement krealloc in a generic
way.
Implement krealloc in mm/util.c and drop slab specific implementations of
krealloc.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The function we are calling to initialize object debug state during early NUMA
bootstrap sets up an inactive object giving it the wrong redzone signature.
The bootstrap nodes are active objects and should have active redzone
signatures.
Currently slab validation complains and reverts the object to active state.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently SLUB has no provision to deal with too high page orders that may
be specified on the kernel boot line. If an order higher than 6 (on a 4k
platform) is generated then we will BUG() because slabs get more than 65535
objects.
Add some logic that decreases order for slabs that have too many objects.
This allow booting with slab sizes up to MAX_ORDER.
For example
slub_min_order=10
will boot with a default slab size of 4M and reduce slab sizes for small
object sizes to lower orders if the number of objects becomes too big.
Large slab sizes like that allow a concentration of objects of the same
slab cache under as few as possible TLB entries and thus potentially
reduces TLB pressure.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We currently have to do an GFP_ATOMIC allocation because the list_lock is
already taken when we first allocate memory for tracking allocation
information. It would be better if we could avoid atomic allocations.
Allocate a size of the tracking table that is usually sufficient (one page)
before we take the list lock. We will then only do the atomic allocation
if we need to resize the table to become larger than a page (mostly only
needed under large NUMA because of the tracking of cpus and nodes otherwise
the table stays small).
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Use list_for_each_entry() instead of list_for_each().
Get rid of for_all_slabs(). It had only one user. So fold it into the
callback. This also gets rid of cpu_slab_flush.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Changes the error reporting format to loosely follow lockdep.
If data corruption is detected then we generate the following lines:
============================================
BUG <slab-cache>: <problem>
--------------------------------------------
INFO: <more information> [possibly multiple times]
<object dump>
FIX <slab-cache>: <remedial action>
This also adds some more intelligence to the data corruption detection. Its
now capable of figuring out the start and end.
Add a comment on how to configure SLUB so that a production system may
continue to operate even though occasional slab corruption occur through
a misbehaving kernel component. See "Emergency operations" in
Documentation/vm/slub.txt.
[akpm@linux-foundation.org: build fix]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add a new configuration variable
CONFIG_SLUB_DEBUG_ON
If set then the kernel will be booted by default with slab debugging
switched on. Similar to CONFIG_SLAB_DEBUG. By default slab debugging
is available but must be enabled by specifying "slub_debug" as a
kernel parameter.
Also add support to switch off slab debugging for a kernel that was
built with CONFIG_SLUB_DEBUG_ON. This works by specifying
slub_debug=-
as a kernel parameter.
Dave Jones wanted this feature.
http://marc.info/?l=linux-kernel&m=118072189913045&w=2
[akpm@linux-foundation.org: clean up switch statement]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kmem_cache_open is static. EXPORT_SYMBOL was leftover from some earlier
time period where kmem_cache_open was usable outside of slub.
(Fixes powerpc build error)
Signed-off-by: Chrsitoph Lameter <clameter@sgi.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If we move the local_irq_enable() to the end of the function then
add_partial() in early_kmem_cache_node_alloc() will be called
with interrupts disabled like during regular operations.
This makes lockdep happy.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Tested-by: Andre Noll <maan@systemlinux.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If slabs are allocated or freed from a large set of call sites (typical for
the kmalloc area) then we may create more output than fits into a single
PAGE and sysfs only gives us one page. The output should be truncated.
This patch fixes the checks to do the truncation properly.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If ARCH_KMALLOC_MINALIGN is set to a value greater than 8 (SLUBs smallest
kmalloc cache) then SLUB may generate duplicate slabs in sysfs (yes again)
because the object size is padded to reach ARCH_KMALLOC_MINALIGN. Thus the
size of the small slabs is all the same.
No arch sets ARCH_KMALLOC_MINALIGN larger than 8 though except mips which
for some reason wants a 128 byte alignment.
This patch increases the size of the smallest cache if
ARCH_KMALLOC_MINALIGN is greater than 8. In that case more and more of the
smallest caches are disabled.
If we do that then the count of the active general caches that is displayed
on boot is not correct anymore since we may skip elements of the kmalloc
array. So count them separately.
This approach was tested by Havard yesterday.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The data structure to manage the information gathered about functions
allocating and freeing objects is allocated when the list_lock has already
been taken. We need to allocate with GFP_ATOMIC instead of GFP_KERNEL.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Instead of returning the smallest available object return ZERO_SIZE_PTR.
A ZERO_SIZE_PTR can be legitimately used as an object pointer as long as it
is not deferenced. The dereference of ZERO_SIZE_PTR causes a distinctive
fault. kfree can handle a ZERO_SIZE_PTR in the same way as NULL.
This enables functions to use zero sized object. e.g. n = number of objects.
objects = kmalloc(n * sizeof(object));
for (i = 0; i < n; i++)
objects[i].x = y;
kfree(objects);
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Hotplug callbacks are performed with interrupts enabled. Slub requires
interrupts to be disabled for flushing caches.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We need this patch in ASAP. Patch fixes the mysterious hang that remained
on some particular configurations with lockdep on after the first fix that
moved the #idef CONFIG_SLUB_DEBUG to the right location. See
http://marc.info/?t=117963072300001&r=1&w=2
The kmem_cache_node cache is very special because it is needed for NUMA
bootstrap. Under certain conditions (like for example if lockdep is
enabled and significantly increases the size of spinlock_t) the structure
may become exactly the size as one of the larger caches in the kmalloc
array.
That early during bootstrap we cannot perform merging properly. The unique
id for the kmem_cache_node cache will match one of the kmalloc array.
Sysfs will complain about a duplicate directory entry. All of this occurs
while the console is not yet fully operational. Thus boot may appear to be
silently failing.
The kmem_cache_node cache is very special. During early boostrap the main
allocation function is not operational yet and so we have to run our own
small special alloc function during early boot. It is also special in that
it is never freed.
We really do not want any merging on that cache. Set the refcount -1 and
forbid merging of slabs that have a negative refcount.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The check for super sized slabs where we can no longer move the free
pointer behind the object for debugging purposes etc is accessing a
field that is not setup yet. We must use objsize here since the size of
the slab has not been determined yet.
The effect of this is that a global slab shrink via "slabinfo -s" will
show errors about offsets being wrong if booted with slub_debug.
Potentially there are other troubles with huge slabs under slub_debug
because the calculated free pointer offset is truncated.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The object size calculation is wrong if !CONFIG_SLUB_DEBUG because the
#ifdef CONFIG_SLUB_DEBUG is now switching off the size adjustments for
DESTROY_BY_RCU and ctor.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Consolidate functionality into the #ifdef section.
Extract tracing into one subroutine.
Move object debug processing into the #ifdef section so that the
code in __slab_alloc and __slab_free becomes minimal.
Reduce number of functions we need to provide stubs for in the !SLUB_DEBUG case.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
SLAB_CTOR_CONSTRUCTOR is always specified. No point in checking it.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Steven French <sfrench@us.ibm.com>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Dave Kleikamp <shaggy@austin.ibm.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Anton Altaparmakov <aia21@cantab.net>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@ucw.cz>
Cc: David Chinner <dgc@sgi.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The atomicity when handling flags in SLUB is not necessary since both flags
used by SLUB are not updated in a racy way. Flag updates are either done
during slab creation or destruction or under slab_lock. Some of these flags
do not have the non atomic variants that we need. So define our own.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Use inline functions to access the per cpu bit. Intoduce the notion of
"freezing" a slab to make things more understandable.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
There is no user of destructors left. There is no reason why we should keep
checking for destructors calls in the slab allocators.
The RFC for this patch was discussed at
http://marc.info/?l=linux-kernel&m=117882364330705&w=2
Destructors were mainly used for list management which required them to take a
spinlock. Taking a spinlock in a destructor is a bit risky since the slab
allocators may run the destructors anytime they decide a slab is no longer
needed.
Patch drops destructor support. Any attempt to use a destructor will BUG().
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kmem_cache_create() was swapping ctor and dtor in calling find_mergeable():
though it caused no bug, and probably never would, even if destructors are
retained; but fix it so as not to generate anxiety ;)
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This was in SLUB in order to head off trouble while the nr_cpu_ids
functionality was not merged. Its merged now so no need to still have this.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Avoid atomic overhead in slab_alloc and slab_free
SLUB needs to use the slab_lock for the per cpu slabs to synchronize with
potential kfree operations. This patch avoids that need by moving all free
objects onto a lockless_freelist. The regular freelist continues to exist
and will be used to free objects. So while we consume the
lockless_freelist the regular freelist may build up objects.
If we are out of objects on the lockless_freelist then we may check the
regular freelist. If it has objects then we move those over to the
lockless_freelist and do this again. There is a significant savings in
terms of atomic operations that have to be performed.
We can even free directly to the lockless_freelist if we know that we are
running on the same processor. So this speeds up short lived objects.
They may be allocated and freed without taking the slab_lock. This is
particular good for netperf.
In order to maximize the effect of the new faster hotpath we extract the
hottest performance pieces into inlined functions. These are then inlined
into kmem_cache_alloc and kmem_cache_free. So hotpath allocation and
freeing no longer requires a subroutine call within SLUB.
[I am not sure that it is worth doing this because it changes the easy to
read structure of slub just to reduce atomic ops. However, there is
someone out there with a benchmark on 4 way and 8 way processor systems
that seems to show a 5% regression vs. Slab. Seems that the regression is
due to increased atomic operations use vs. SLAB in SLUB). I wonder if
this is applicable or discernable at all in a real workload?]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Currently the slab allocators contain callbacks into the page allocator to
perform the draining of pagesets on remote nodes. This requires SLUB to have
a whole subsystem in order to be compatible with SLAB. Moving node draining
out of the slab allocators avoids a section of code in SLUB.
Move the node draining so that is is done when the vm statistics are updated.
At that point we are already touching all the cachelines with the pagesets of
a processor.
Add a expire counter there. If we have to update per zone or global vm
statistics then assume that the pageset will require subsequent draining.
The expire counter will be decremented on each vm stats update pass until it
reaches zero. Then we will drain one batch from the pageset. The draining
will cause vm counter updates which will then cause another expiration until
the pcp is empty. So we will drain a batch every 3 seconds.
Note that remote node draining is a somewhat esoteric feature that is required
on large NUMA systems because otherwise significant portions of system memory
can become trapped in pcp queues. The number of pcp is determined by the
number of processors and nodes in a system. A system with 4 processors and 2
nodes has 8 pcps which is okay. But a system with 1024 processors and 512
nodes has 512k pcps with a high potential for large amount of memory being
caught in them.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
vmstat is currently using the cache reaper to periodically bring the
statistics up to date. The cache reaper does only exists in SLUB as a way to
provide compatibility with SLAB. This patch removes the vmstat calls from the
slab allocators and provides its own handling.
The advantage is also that we can use a different frequency for the updates.
Refreshing vm stats is a pretty fast job so we can run this every second and
stagger this by only one tick. This will lead to some overlap in large
systems. F.e a system running at 250 HZ with 1024 processors will have 4 vm
updates occurring at once.
However, the vm stats update only accesses per node information. It is only
necessary to stagger the vm statistics updates per processor in each node. Vm
counter updates occurring on distant nodes will not cause cacheline
contention.
We could implement an alternate approach that runs the first processor on each
node at the second and then each of the other processor on a node on a
subsequent tick. That may be useful to keep a large amount of the second free
of timer activity. Maybe the timer folks will have some feedback on this one?
[jirislaby@gmail.com: add missing break]
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Since nonboot CPUs are now disabled after tasks and devices have been
frozen and the CPU hotplug infrastructure is used for this purpose, we need
special CPU hotplug notifications that will help the CPU-hotplug-aware
subsystems distinguish normal CPU hotplug events from CPU hotplug events
related to a system-wide suspend or resume operation in progress. This
patch introduces such notifications and causes them to be used during
suspend and resume transitions. It also changes all of the
CPU-hotplug-aware subsystems to take these notifications into consideration
(for now they are handled in the same way as the corresponding "normal"
ones).
[oleg@tv-sign.ru: cleanups]
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
No "blank" (or "*") line is allowed between the function name and lines for
it parameter(s).
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
In some cases SLUB is creating uselessly slabs that are larger than
slub_max_order. Also the layout of some of the slabs was not satisfactory.
Go to an iterarive approach.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CONFIG_SLUB_DEBUG can be used to switch off the debugging and sysfs components
of SLUB. Thus SLUB will be able to replace SLOB. SLUB can arrange objects in
a denser way than SLOB and the code size should be minimal without debugging
and sysfs support.
Note that CONFIG_SLUB_DEBUG is materially different from CONFIG_SLAB_DEBUG.
CONFIG_SLAB_DEBUG is used to enable slab debugging in SLAB. SLUB enables
debugging via a boot parameter. SLUB debug code should always be present.
CONFIG_SLUB_DEBUG can be modified in the embedded config section.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Move the tracking definitions and the check_valid_pointer() function away from
the debugging related functions.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Trace in both slab_alloc and slab_free has a lot of common code. Use a single
function for both.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This replaces the PageError() checking. DebugSlab is clearer and allows for
future changes to the page bit used. We also need it to support
CONFIG_SLUB_DEBUG.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Move the resiliency check into the SYSFS section after validate_slab that is
used by the resiliency check. This will avoid a forward declaration.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Scanning of objects happens in a number of functions. Consolidate that code.
DECLARE_BITMAP instead of coding the declaration for bitmaps.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Update comments throughout SLUB to reflect the new developments. Fix up
various awkward sentences.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Its only purpose was to bring some sort of symmetry to sysfs usage when
dealing with bootstrapping per cpu flushing. Since we do not time out slabs
anymore we have no need to run finish_bootstrap even without sysfs. Fold it
back into slab_sysfs_init and drop the initcall for the !SYFS case.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We really do not need all this gaga there.
ksize gives us all the information we need to figure out if the object can
cope with the new size.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We needlessly duplicate code. Also make check_valid_pointer inline.
Signed-off-by: Christoph LAemter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If no redzoning is selected then we do not need padding before the next
object.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
SLUB currently assumes that the cacheline size is static. However, i386 f.e.
supports dynamic cache line size determination.
Use cache_line_size() instead of L1_CACHE_BYTES in the allocator.
That also explains the purpose of SLAB_HWCACHE_ALIGN. So we will need to keep
that one around to allow dynamic aligning of objects depending on boot
determination of the cache line size.
[akpm@linux-foundation.org: need to define it before we use it]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The newly merged SLUB allocator patches had been generated before the
removal of "struct subsystem", and ended up applying fine, but wouldn't
build based on the current tree as a result.
Fix up that merge error - not that SLUB is likely really ready for
showtime yet, but at least I can fix the trivial stuff.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
There is no user remaining and I have never seen any use of that flag.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
SLAB_CTOR atomic is never used which is no surprise since I cannot imagine
that one would want to do something serious in a constructor or destructor.
In particular given that the slab allocators run with interrupts disabled.
Actions in constructors and destructors are by their nature very limited
and usually do not go beyond initializing variables and list operations.
(The i386 pgd ctor and dtors do take a spinlock in constructor and
destructor..... I think that is the furthest we go at this point.)
There is no flag passed to the destructor so removing SLAB_CTOR_ATOMIC also
establishes a certain symmetry.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
I have never seen a use of SLAB_DEBUG_INITIAL. It is only supported by
SLAB.
I think its purpose was to have a callback after an object has been freed
to verify that the state is the constructor state again? The callback is
performed before each freeing of an object.
I would think that it is much easier to check the object state manually
before the free. That also places the check near the code object
manipulation of the object.
Also the SLAB_DEBUG_INITIAL callback is only performed if the kernel was
compiled with SLAB debugging on. If there would be code in a constructor
handling SLAB_DEBUG_INITIAL then it would have to be conditional on
SLAB_DEBUG otherwise it would just be dead code. But there is no such code
in the kernel. I think SLUB_DEBUG_INITIAL is too problematic to make real
use of, difficult to understand and there are easier ways to accomplish the
same effect (i.e. add debug code before kfree).
There is a related flag SLAB_CTOR_VERIFY that is frequently checked to be
clear in fs inode caches. Remove the pointless checks (they would even be
pointless without removeal of SLAB_DEBUG_INITIAL) from the fs constructors.
This is the last slab flag that SLUB did not support. Remove the check for
unimplemented flags from SLUB.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This patch was recently posted to lkml and acked by Pekka.
The flag SLAB_MUST_HWCACHE_ALIGN is
1. Never checked by SLAB at all.
2. A duplicate of SLAB_HWCACHE_ALIGN for SLUB
3. Fulfills the role of SLAB_HWCACHE_ALIGN for SLOB.
The only remaining use is in sparc64 and ppc64 and their use there
reflects some earlier role that the slab flag once may have had. If
its specified then SLAB_HWCACHE_ALIGN is also specified.
The flag is confusing, inconsistent and has no purpose.
Remove it.
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Make sure that the check function really only check things and do not perform
activities. Extract the tracing and object seeding out of the two check
functions and place them into slab_alloc and slab_free
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
At kmem_cache_shrink check if we have any empty slabs on the partial
if so then remove them.
Also--as an anti-fragmentation measure--sort the partial slabs so that
the most fully allocated ones come first and the least allocated last.
The next allocations may fill up the nearly full slabs. Having the
least allocated slabs last gives them the maximum chance that their
remaining objects may be freed. Thus we can hopefully minimize the
partial slabs.
I think this is the best one can do in terms antifragmentation
measures. Real defragmentation (meaning moving objects out of slabs with
the least free objects to those that are almost full) can be implemted
by reverse scanning through the list produced here but that would mean
that we need to provide a callback at slab cache creation that allows
the deletion or moving of an object. This will involve slab API
changes, so defer for now.
Cc: Mel Gorman <mel@skynet.ie>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This patch enables listing the callers who allocated or freed objects in a
cache.
For example to list the allocators for kmalloc-128 do
cat /sys/slab/kmalloc-128/alloc_calls
7 sn_io_slot_fixup+0x40/0x700
7 sn_io_slot_fixup+0x80/0x700
9 sn_bus_fixup+0xe0/0x380
6 param_sysfs_setup+0xf0/0x280
276 percpu_populate+0xf0/0x1a0
19 __register_chrdev_region+0x30/0x360
8 expand_files+0x2e0/0x6e0
1 sys_epoll_create+0x60/0x200
1 __mounts_open+0x140/0x2c0
65 kmem_alloc+0x110/0x280
3 alloc_disk_node+0xe0/0x200
33 as_get_io_context+0x90/0x280
74 kobject_kset_add_dir+0x40/0x140
12 pci_create_bus+0x2a0/0x5c0
1 acpi_ev_create_gpe_block+0x120/0x9e0
41 con_insert_unipair+0x100/0x1c0
1 uart_open+0x1c0/0xba0
1 dma_pool_create+0xe0/0x340
2 neigh_table_init_no_netlink+0x260/0x4c0
6 neigh_parms_alloc+0x30/0x200
1 netlink_kernel_create+0x130/0x320
5 fz_hash_alloc+0x50/0xe0
2 sn_common_hubdev_init+0xd0/0x6e0
28 kernel_param_sysfs_setup+0x30/0x180
72 process_zones+0x70/0x2e0
cat /sys/slab/kmalloc-128/free_calls
558 <not-available>
3 sn_io_slot_fixup+0x600/0x700
84 free_fdtable_rcu+0x120/0x260
2 seq_release+0x40/0x60
6 kmem_free+0x70/0xc0
24 free_as_io_context+0x20/0x200
1 acpi_get_object_info+0x3a0/0x3e0
1 acpi_add_single_object+0xcf0/0x1e40
2 con_release_unimap+0x80/0x140
1 free+0x20/0x40
SLAB_STORE_USER must be enabled for a slab cache by either booting with
"slab_debug" or enabling user tracking specifically for the slab of interest.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
We leave a mininum of partial slabs on nodes when we search for
partial slabs on other node. Define a constant for that value.
Then modify slub to keep MIN_PARTIAL slabs around.
This avoids bad situations where a function frees the last object
in a slab (which results in the page being returned to the page
allocator) only to then allocate one again (which requires getting
a page back from the page allocator if the partial list was empty).
Keeping a couple of slabs on the partial list reduces overhead.
Empty slabs are added to the end of the partial list to insure that
partially allocated slabs are consumed first (defragmentation).
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This enables validation of slab. Validation means that all objects are
checked to see if there are redzone violations, if padding has been
overwritten or any pointers have been corrupted. Also checks the consistency
of slab counters.
Validation enables the detection of metadata corruption without the kernel
having to execute code that actually uses (allocs/frees) and object. It
allows one to make sure that the slab metainformation and the guard values
around an object have not been compromised.
A single slabcache can be checked by writing a 1 to the "validate" file.
i.e.
echo 1 >/sys/slab/kmalloc-128/validate
or use the slabinfo tool to check all slabs
slabinfo -v
Error messages will show up in the syslog.
Note that validation can only reach slabs that are on a list. This means that
we are usually restricted to partial slabs and active slabs unless
SLAB_STORE_USER is active which will build a full slab list and allows
validation of slabs that are fully in use. Booting with "slub_debug" set will
enable SLAB_STORE_USER and then full diagnostic are available.
Note that we attempt to push cpu slabs back to the lists when we start the
check. If the cpu slab is reactivated before we get to it (another processor
grabs it before we get to it) then it cannot be checked.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If slab tracking is on then build a list of full slabs so that we can verify
the integrity of all slabs and are also able to built list of alloc/free
callers.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Object tracking did not work the right way for several call chains. Fix this up
by adding a new parameter to slub_alloc and slub_free that specifies the
caller address explicitly.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If we add a new flag so that we can distinguish between the first page and the
tail pages then we can avoid to use page->private in the first page.
page->private == page for the first page, so there is no real information in
there.
Freeing up page->private makes the use of compound pages more transparent.
They become more usable like real pages. Right now we have to be careful f.e.
if we are going beyond PAGE_SIZE allocations in the slab on i386 because we
can then no longer use the private field. This is one of the issues that
cause us not to support debugging for page size slabs in SLAB.
Having page->private available for SLUB would allow more meta information in
the page struct. I can probably avoid the 16 bit ints that I have in there
right now.
Also if page->private is available then a compound page may be equipped with
buffer heads. This may free up the way for filesystems to support larger
blocks than page size.
We add PageTail as an alias of PageReclaim. Compound pages cannot currently
be reclaimed. Because of the alias one needs to check PageCompound first.
The RFC for the this approach was discussed at
http://marc.info/?t=117574302800001&r=1&w=2
[nacc@us.ibm.com: fix hugetlbfs]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Makes SLUB behave like SLAB in this area to avoid issues....
Throw a stack dump to alert people.
At some point the behavior should be switched back. NULL is no memory as
far as I can tell and if the use asked for 0 bytes then he need to get no
memory.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Structures may contain u64 items on 32 bit platforms that are only able to
address 64 bit items on 64 bit boundaries. Change the mininum alignment of
slabs to conform to those expectations.
ARCH_KMALLOC_MINALIGN must be changed for good since a variety of structure
are mixed in the general slabs.
ARCH_SLAB_MINALIGN is changed because currently there is no consistent
specification of object alignment. We may have that in the future when the
KMEM_CACHE and related macros are used to generate slabs. These pass the
alignment of the structure generated by the compiler to the slab.
With KMEM_CACHE etc we could align structures that do not contain 64
bit values to 32 bit boundaries potentially saving some memory.
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is a new slab allocator which was motivated by the complexity of the
existing code in mm/slab.c. It attempts to address a variety of concerns
with the existing implementation.
A. Management of object queues
A particular concern was the complex management of the numerous object
queues in SLAB. SLUB has no such queues. Instead we dedicate a slab for
each allocating CPU and use objects from a slab directly instead of
queueing them up.
B. Storage overhead of object queues
SLAB Object queues exist per node, per CPU. The alien cache queue even
has a queue array that contain a queue for each processor on each
node. For very large systems the number of queues and the number of
objects that may be caught in those queues grows exponentially. On our
systems with 1k nodes / processors we have several gigabytes just tied up
for storing references to objects for those queues This does not include
the objects that could be on those queues. One fears that the whole
memory of the machine could one day be consumed by those queues.
C. SLAB meta data overhead
SLAB has overhead at the beginning of each slab. This means that data
cannot be naturally aligned at the beginning of a slab block. SLUB keeps
all meta data in the corresponding page_struct. Objects can be naturally
aligned in the slab. F.e. a 128 byte object will be aligned at 128 byte
boundaries and can fit tightly into a 4k page with no bytes left over.
SLAB cannot do this.
D. SLAB has a complex cache reaper
SLUB does not need a cache reaper for UP systems. On SMP systems
the per CPU slab may be pushed back into partial list but that
operation is simple and does not require an iteration over a list
of objects. SLAB expires per CPU, shared and alien object queues
during cache reaping which may cause strange hold offs.
E. SLAB has complex NUMA policy layer support
SLUB pushes NUMA policy handling into the page allocator. This means that
allocation is coarser (SLUB does interleave on a page level) but that
situation was also present before 2.6.13. SLABs application of
policies to individual slab objects allocated in SLAB is
certainly a performance concern due to the frequent references to
memory policies which may lead a sequence of objects to come from
one node after another. SLUB will get a slab full of objects
from one node and then will switch to the next.
F. Reduction of the size of partial slab lists
SLAB has per node partial lists. This means that over time a large
number of partial slabs may accumulate on those lists. These can
only be reused if allocator occur on specific nodes. SLUB has a global
pool of partial slabs and will consume slabs from that pool to
decrease fragmentation.
G. Tunables
SLAB has sophisticated tuning abilities for each slab cache. One can
manipulate the queue sizes in detail. However, filling the queues still
requires the uses of the spin lock to check out slabs. SLUB has a global
parameter (min_slab_order) for tuning. Increasing the minimum slab
order can decrease the locking overhead. The bigger the slab order the
less motions of pages between per CPU and partial lists occur and the
better SLUB will be scaling.
G. Slab merging
We often have slab caches with similar parameters. SLUB detects those
on boot up and merges them into the corresponding general caches. This
leads to more effective memory use. About 50% of all caches can
be eliminated through slab merging. This will also decrease
slab fragmentation because partial allocated slabs can be filled
up again. Slab merging can be switched off by specifying
slub_nomerge on boot up.
Note that merging can expose heretofore unknown bugs in the kernel
because corrupted objects may now be placed differently and corrupt
differing neighboring objects. Enable sanity checks to find those.
H. Diagnostics
The current slab diagnostics are difficult to use and require a
recompilation of the kernel. SLUB contains debugging code that
is always available (but is kept out of the hot code paths).
SLUB diagnostics can be enabled via the "slab_debug" option.
Parameters can be specified to select a single or a group of
slab caches for diagnostics. This means that the system is running
with the usual performance and it is much more likely that
race conditions can be reproduced.
I. Resiliency
If basic sanity checks are on then SLUB is capable of detecting
common error conditions and recover as best as possible to allow the
system to continue.
J. Tracing
Tracing can be enabled via the slab_debug=T,<slabcache> option
during boot. SLUB will then protocol all actions on that slabcache
and dump the object contents on free.
K. On demand DMA cache creation.
Generally DMA caches are not needed. If a kmalloc is used with
__GFP_DMA then just create this single slabcache that is needed.
For systems that have no ZONE_DMA requirement the support is
completely eliminated.
L. Performance increase
Some benchmarks have shown speed improvements on kernbench in the
range of 5-10%. The locking overhead of slub is based on the
underlying base allocation size. If we can reliably allocate
larger order pages then it is possible to increase slub
performance much further. The anti-fragmentation patches may
enable further performance increases.
Tested on:
i386 UP + SMP, x86_64 UP + SMP + NUMA emulation, IA64 NUMA + Simulator
SLUB Boot options
slub_nomerge Disable merging of slabs
slub_min_order=x Require a minimum order for slab caches. This
increases the managed chunk size and therefore
reduces meta data and locking overhead.
slub_min_objects=x Mininum objects per slab. Default is 8.
slub_max_order=x Avoid generating slabs larger than order specified.
slub_debug Enable all diagnostics for all caches
slub_debug=<options> Enable selective options for all caches
slub_debug=<o>,<cache> Enable selective options for a certain set of
caches
Available Debug options
F Double Free checking, sanity and resiliency
R Red zoning
P Object / padding poisoning
U Track last free / alloc
T Trace all allocs / frees (only use for individual slabs).
To use SLUB: Apply this patch and then select SLUB as the default slab
allocator.
[hugh@veritas.com: fix an oops-causing locking error]
[akpm@linux-foundation.org: various stupid cleanups and small fixes]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Christoph Lameter