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cleancache: remove limit on the number of cleancache enabled filesystems 

The limit equals 32 and is imposed by the number of entries in the
fs_poolid_map and shared_fs_poolid_map.  Nowadays it is insufficient,
because with containers on board a Linux host can have hundreds of
active fs mounts.

These maps were introduced by commit 49a9ab815a ("mm: cleancache:
lazy initialization to allow tmem backends to build/run as modules") in
order to allow compiling cleancache drivers as modules.  Real pool ids
are stored in these maps while super_block->cleancache_poolid points to
an entry in the map, so that on cleancache registration we can walk over
all (if there are <= 32 of them, of course) cleancache-enabled super
blocks and assign real pool ids.

Actually, there is absolutely no need in these maps, because we can
iterate over all super blocks immediately using iterate_supers.  This is
not racy, because cleancache_init_ops is called from mount_fs with
super_block->s_umount held for writing, while iterate_supers takes this
semaphore for reading, so if we call iterate_supers after setting
cleancache_ops, all super blocks that had been created before
cleancache_register_ops was called will be assigned pool ids by the
action function of iterate_supers while all newer super blocks will
receive it in cleancache_init_fs.

This patch therefore removes the maps and hence the artificial limit on
the number of cleancache enabled filesystems.

Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Stefan Hengelein <ilendir@googlemail.com>
Cc: Florian Schmaus <fschmaus@gmail.com>
Cc: Andor Daam <andor.daam@googlemail.com>
Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vladimir Davydov 2015-04-14 15:46:48 -07:00 committed by Linus Torvalds
parent 53d85c9856
commit 3cb29d1117
3 changed files with 94 additions and 182 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/super.c
View File

@ -224,7 +224,7 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
s->s_maxbytes = MAX_NON_LFS;
s->s_op = &default_op;
s->s_time_gran = 1000000000;
s->cleancache_poolid = -1;
s->cleancache_poolid = CLEANCACHE_NO_POOL;
s->s_shrink.seeks = DEFAULT_SEEKS;
s->s_shrink.scan_objects = super_cache_scan;

4
include/linux/cleancache.h
View File

@ -5,6 +5,10 @@
#include <linux/exportfs.h>
#include <linux/mm.h>
#define CLEANCACHE_NO_POOL -1
#define CLEANCACHE_NO_BACKEND -2
#define CLEANCACHE_NO_BACKEND_SHARED -3
#define CLEANCACHE_KEY_MAX 6
/*

270
mm/cleancache.c
View File

@ -19,7 +19,7 @@
#include <linux/cleancache.h>
/*
* cleancache_ops is set by cleancache_ops_register to contain the pointers
* cleancache_ops is set by cleancache_register_ops to contain the pointers
* to the cleancache "backend" implementation functions.
*/
static struct cleancache_ops *cleancache_ops __read_mostly;
@ -34,104 +34,78 @@ static u64 cleancache_failed_gets;
static u64 cleancache_puts;
static u64 cleancache_invalidates;
/*
* When no backend is registered all calls to init_fs and init_shared_fs
* are registered and fake poolids (FAKE_FS_POOLID_OFFSET or
* FAKE_SHARED_FS_POOLID_OFFSET, plus offset in the respective array
* [shared_|]fs_poolid_map) are given to the respective super block
* (sb->cleancache_poolid) and no tmem_pools are created. When a backend
* registers with cleancache the previous calls to init_fs and init_shared_fs
* are executed to create tmem_pools and set the respective poolids. While no
* backend is registered all "puts", "gets" and "flushes" are ignored or failed.
*/
#define MAX_INITIALIZABLE_FS 32
#define FAKE_FS_POOLID_OFFSET 1000
#define FAKE_SHARED_FS_POOLID_OFFSET 2000
#define FS_NO_BACKEND (-1)
#define FS_UNKNOWN (-2)
static int fs_poolid_map[MAX_INITIALIZABLE_FS];
static int shared_fs_poolid_map[MAX_INITIALIZABLE_FS];
static char *uuids[MAX_INITIALIZABLE_FS];
/*
* Mutex for the [shared_|]fs_poolid_map to guard against multiple threads
* invoking umount (and ending in __cleancache_invalidate_fs) and also multiple
* threads calling mount (and ending up in __cleancache_init_[shared|]fs).
*/
static DEFINE_MUTEX(poolid_mutex);
/*
* When set to false (default) all calls to the cleancache functions, except
* the __cleancache_invalidate_fs and __cleancache_init_[shared|]fs are guarded
* by the if (!cleancache_ops) return. This means multiple threads (from
* different filesystems) will be checking cleancache_ops. The usage of a
* bool instead of a atomic_t or a bool guarded by a spinlock is OK - we are
* OK if the time between the backend's have been initialized (and
* cleancache_ops has been set to not NULL) and when the filesystems start
* actually calling the backends. The inverse (when unloading) is obviously
* not good - but this shim does not do that (yet).
*/
/*
* The backends and filesystems work all asynchronously. This is b/c the
* backends can be built as modules.
* The usual sequence of events is:
* a) mount / -> __cleancache_init_fs is called. We set the
* [shared_|]fs_poolid_map and uuids for.
*
* b). user does I/Os -> we call the rest of __cleancache_* functions
* which return immediately as cleancache_ops is false.
*
* c). modprobe zcache -> cleancache_register_ops. We init the backend
* and set cleancache_ops to true, and for any fs_poolid_map
* (which is set by __cleancache_init_fs) we initialize the poolid.
*
* d). user does I/Os -> now that cleancache_ops is true all the
* __cleancache_* functions can call the backend. They all check
* that fs_poolid_map is valid and if so invoke the backend.
*
* e). umount / -> __cleancache_invalidate_fs, the fs_poolid_map is
* reset (which is the second check in the __cleancache_* ops
* to call the backend).
*
* The sequence of event could also be c), followed by a), and d). and e). The
* c) would not happen anymore. There is also the chance of c), and one thread
* doing a) + d), and another doing e). For that case we depend on the
* filesystem calling __cleancache_invalidate_fs in the proper sequence (so
* that it handles all I/Os before it invalidates the fs (which is last part
* of unmounting process).
*
* Note: The acute reader will notice that there is no "rmmod zcache" case.
* This is b/c the functionality for that is not yet implemented and when
* done, will require some extra locking not yet devised.
*/
static void cleancache_register_ops_sb(struct super_block *sb, void *unused)
{
switch (sb->cleancache_poolid) {
case CLEANCACHE_NO_BACKEND:
__cleancache_init_fs(sb);
break;
case CLEANCACHE_NO_BACKEND_SHARED:
__cleancache_init_shared_fs(sb);
break;
}
}
/*
* Register operations for cleancache. Returns 0 on success.
*/
int cleancache_register_ops(struct cleancache_ops *ops)
{
int i;
mutex_lock(&poolid_mutex);
if (cleancache_ops) {
mutex_unlock(&poolid_mutex);
if (cmpxchg(&cleancache_ops, NULL, ops))
return -EBUSY;
}
for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
if (fs_poolid_map[i] == FS_NO_BACKEND)
fs_poolid_map[i] = ops->init_fs(PAGE_SIZE);
if (shared_fs_poolid_map[i] == FS_NO_BACKEND)
shared_fs_poolid_map[i] = ops->init_shared_fs
(uuids[i], PAGE_SIZE);
}
/*
* We MUST set cleancache_ops _after_ we have called the backends
* init_fs or init_shared_fs functions. Otherwise the compiler might
* re-order where cleancache_ops is set in this function.
* A cleancache backend can be built as a module and hence loaded after
* a cleancache enabled filesystem has called cleancache_init_fs. To
* handle such a scenario, here we call ->init_fs or ->init_shared_fs
* for each active super block. To differentiate between local and
* shared filesystems, we temporarily initialize sb->cleancache_poolid
* to CLEANCACHE_NO_BACKEND or CLEANCACHE_NO_BACKEND_SHARED
* respectively in case there is no backend registered at the time
* cleancache_init_fs or cleancache_init_shared_fs is called.
*
* Since filesystems can be mounted concurrently with cleancache
* backend registration, we have to be careful to guarantee that all
* cleancache enabled filesystems that has been mounted by the time
* cleancache_register_ops is called has got and all mounted later will
* get cleancache_poolid. This is assured by the following statements
* tied together:
*
* a) iterate_supers skips only those super blocks that has started
* ->kill_sb
*
* b) if iterate_supers encounters a super block that has not finished
* ->mount yet, it waits until it is finished
*
* c) cleancache_init_fs is called from ->mount and
* cleancache_invalidate_fs is called from ->kill_sb
*
* d) we call iterate_supers after cleancache_ops has been set
*
* From a) it follows that if iterate_supers skips a super block, then
* either the super block is already dead, in which case we do not need
* to bother initializing cleancache for it, or it was mounted after we
* initiated iterate_supers. In the latter case, it must have seen
* cleancache_ops set according to d) and initialized cleancache from
* ->mount by itself according to c). This proves that we call
* ->init_fs at least once for each active super block.
*
* From b) and c) it follows that if iterate_supers encounters a super
* block that has already started ->init_fs, it will wait until ->mount
* and hence ->init_fs has finished, then check cleancache_poolid, see
* that it has already been set and therefore do nothing. This proves
* that we call ->init_fs no more than once for each super block.
*
* Combined together, the last two paragraphs prove the function
* correctness.
*
* Note that various cleancache callbacks may proceed before this
* function is called or even concurrently with it, but since
* CLEANCACHE_NO_BACKEND is negative, they will all result in a noop
* until the corresponding ->init_fs has been actually called and
* cleancache_ops has been set.
*/
barrier();
cleancache_ops = ops;
mutex_unlock(&poolid_mutex);
iterate_supers(cleancache_register_ops_sb, NULL);
return 0;
}
EXPORT_SYMBOL(cleancache_register_ops);
@ -139,42 +113,28 @@ EXPORT_SYMBOL(cleancache_register_ops);
/* Called by a cleancache-enabled filesystem at time of mount */
void __cleancache_init_fs(struct super_block *sb)
{
int i;
int pool_id = CLEANCACHE_NO_BACKEND;
mutex_lock(&poolid_mutex);
for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
if (fs_poolid_map[i] == FS_UNKNOWN) {
sb->cleancache_poolid = i + FAKE_FS_POOLID_OFFSET;
if (cleancache_ops)
fs_poolid_map[i] = cleancache_ops->init_fs(PAGE_SIZE);
else
fs_poolid_map[i] = FS_NO_BACKEND;
break;
}
if (cleancache_ops) {
pool_id = cleancache_ops->init_fs(PAGE_SIZE);
if (pool_id < 0)
pool_id = CLEANCACHE_NO_POOL;
}
mutex_unlock(&poolid_mutex);
sb->cleancache_poolid = pool_id;
}
EXPORT_SYMBOL(__cleancache_init_fs);
/* Called by a cleancache-enabled clustered filesystem at time of mount */
void __cleancache_init_shared_fs(struct super_block *sb)
{
int i;
int pool_id = CLEANCACHE_NO_BACKEND_SHARED;
mutex_lock(&poolid_mutex);
for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
if (shared_fs_poolid_map[i] == FS_UNKNOWN) {
sb->cleancache_poolid = i + FAKE_SHARED_FS_POOLID_OFFSET;
uuids[i] = sb->s_uuid;
if (cleancache_ops)
shared_fs_poolid_map[i] = cleancache_ops->init_shared_fs
(sb->s_uuid, PAGE_SIZE);
else
shared_fs_poolid_map[i] = FS_NO_BACKEND;
break;
}
if (cleancache_ops) {
pool_id = cleancache_ops->init_shared_fs(sb->s_uuid, PAGE_SIZE);
if (pool_id < 0)
pool_id = CLEANCACHE_NO_POOL;
}
mutex_unlock(&poolid_mutex);
sb->cleancache_poolid = pool_id;
}
EXPORT_SYMBOL(__cleancache_init_shared_fs);
@ -203,19 +163,6 @@ static int cleancache_get_key(struct inode *inode,
return 0;
}
/*
* Returns a pool_id that is associated with a given fake poolid.
*/
static int get_poolid_from_fake(int fake_pool_id)
{
if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET)
return shared_fs_poolid_map[fake_pool_id -
FAKE_SHARED_FS_POOLID_OFFSET];
else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET)
return fs_poolid_map[fake_pool_id - FAKE_FS_POOLID_OFFSET];
return FS_NO_BACKEND;
}
/*
* "Get" data from cleancache associated with the poolid/inode/index
* that were specified when the data was put to cleanache and, if
@ -231,7 +178,6 @@ int __cleancache_get_page(struct page *page)
{
int ret = -1;
int pool_id;
int fake_pool_id;
struct cleancache_filekey key = { .u.key = { 0 } };
if (!cleancache_ops) {
@ -240,17 +186,14 @@ int __cleancache_get_page(struct page *page)
}
VM_BUG_ON_PAGE(!PageLocked(page), page);
fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
if (fake_pool_id < 0)
pool_id = page->mapping->host->i_sb->cleancache_poolid;
if (pool_id < 0)
goto out;
pool_id = get_poolid_from_fake(fake_pool_id);
if (cleancache_get_key(page->mapping->host, &key) < 0)
goto out;
if (pool_id >= 0)
ret = cleancache_ops->get_page(pool_id,
key, page->index, page);
ret = cleancache_ops->get_page(pool_id, key, page->index, page);
if (ret == 0)
cleancache_succ_gets++;
else
@ -273,7 +216,6 @@ EXPORT_SYMBOL(__cleancache_get_page);
void __cleancache_put_page(struct page *page)
{
int pool_id;
int fake_pool_id;
struct cleancache_filekey key = { .u.key = { 0 } };
if (!cleancache_ops) {
@ -282,12 +224,7 @@ void __cleancache_put_page(struct page *page)
}
VM_BUG_ON_PAGE(!PageLocked(page), page);
fake_pool_id = page->mapping->host->i_sb->cleancache_poolid;
if (fake_pool_id < 0)
return;
pool_id = get_poolid_from_fake(fake_pool_id);
pool_id = page->mapping->host->i_sb->cleancache_poolid;
if (pool_id >= 0 &&
cleancache_get_key(page->mapping->host, &key) >= 0) {
cleancache_ops->put_page(pool_id, key, page->index, page);
@ -308,18 +245,13 @@ void __cleancache_invalidate_page(struct address_space *mapping,
struct page *page)
{
/* careful... page->mapping is NULL sometimes when this is called */
int pool_id;
int fake_pool_id = mapping->host->i_sb->cleancache_poolid;
int pool_id = mapping->host->i_sb->cleancache_poolid;
struct cleancache_filekey key = { .u.key = { 0 } };
if (!cleancache_ops)
return;
if (fake_pool_id >= 0) {
pool_id = get_poolid_from_fake(fake_pool_id);
if (pool_id < 0)
return;
if (pool_id >= 0) {
VM_BUG_ON_PAGE(!PageLocked(page), page);
if (cleancache_get_key(mapping->host, &key) >= 0) {
cleancache_ops->invalidate_page(pool_id,
@ -341,18 +273,12 @@ EXPORT_SYMBOL(__cleancache_invalidate_page);
*/
void __cleancache_invalidate_inode(struct address_space *mapping)
{
int pool_id;
int fake_pool_id = mapping->host->i_sb->cleancache_poolid;
int pool_id = mapping->host->i_sb->cleancache_poolid;
struct cleancache_filekey key = { .u.key = { 0 } };
if (!cleancache_ops)
return;
if (fake_pool_id < 0)
return;
pool_id = get_poolid_from_fake(fake_pool_id);
if (pool_id >= 0 && cleancache_get_key(mapping->host, &key) >= 0)
cleancache_ops->invalidate_inode(pool_id, key);
}
@ -365,32 +291,18 @@ EXPORT_SYMBOL(__cleancache_invalidate_inode);
*/
void __cleancache_invalidate_fs(struct super_block *sb)
{
int index;
int fake_pool_id = sb->cleancache_poolid;
int old_poolid = fake_pool_id;
int pool_id;
mutex_lock(&poolid_mutex);
if (fake_pool_id >= FAKE_SHARED_FS_POOLID_OFFSET) {
index = fake_pool_id - FAKE_SHARED_FS_POOLID_OFFSET;
old_poolid = shared_fs_poolid_map[index];
shared_fs_poolid_map[index] = FS_UNKNOWN;
uuids[index] = NULL;
} else if (fake_pool_id >= FAKE_FS_POOLID_OFFSET) {
index = fake_pool_id - FAKE_FS_POOLID_OFFSET;
old_poolid = fs_poolid_map[index];
fs_poolid_map[index] = FS_UNKNOWN;
}
sb->cleancache_poolid = -1;
if (cleancache_ops)
cleancache_ops->invalidate_fs(old_poolid);
mutex_unlock(&poolid_mutex);
pool_id = sb->cleancache_poolid;
sb->cleancache_poolid = CLEANCACHE_NO_POOL;
if (cleancache_ops && pool_id >= 0)
cleancache_ops->invalidate_fs(pool_id);
}
EXPORT_SYMBOL(__cleancache_invalidate_fs);
static int __init init_cleancache(void)
{
int i;
#ifdef CONFIG_DEBUG_FS
struct dentry *root = debugfs_create_dir("cleancache", NULL);
if (root == NULL)
@ -402,10 +314,6 @@ static int __init init_cleancache(void)
debugfs_create_u64("invalidates", S_IRUGO,
root, &cleancache_invalidates);
#endif
for (i = 0; i < MAX_INITIALIZABLE_FS; i++) {
fs_poolid_map[i] = FS_UNKNOWN;
shared_fs_poolid_map[i] = FS_UNKNOWN;
}
return 0;
}
module_init(init_cleancache)