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Merge branch 'akpm' (rest of patches from Andrew) 

Merge the left-over patches from Andrew Morton.

This merges the remaining two patches from Andrew's pile of "little bit
more MM".  I mulled it over, and we emailed back and forth with Josef,
and he pointed out where I was wrong.

Rule #51 of kernel maintenance: when somebody makes it clear that they
know the code better than you did, stop arguing and just apply the damn
patch.

Add a third patch by me to add a comment for the case that I had thought
was buggy and Josef corrected me on.

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  filemap: add a comment about FAULT_FLAG_RETRY_NOWAIT behavior
  filemap: drop the mmap_sem for all blocking operations
  filemap: kill page_cache_read usage in filemap_fault
This commit is contained in:
Linus Torvalds 2019-03-15 12:00:45 -07:00
parent f261c4e529 8b0f9fa2e0
commit f91f2ee54a
2 changed files with 134 additions and 75 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/pagemap.h
View File

@ -239,6 +239,7 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
#define FGP_WRITE 0x00000008
#define FGP_NOFS 0x00000010
#define FGP_NOWAIT 0x00000020
#define FGP_FOR_MMAP 0x00000040
struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
int fgp_flags, gfp_t cache_gfp_mask);

208
mm/filemap.c
View File

@ -1587,6 +1587,9 @@ EXPORT_SYMBOL(find_lock_entry);
* @gfp_mask and added to the page cache and the VM's LRU
* list. The page is returned locked and with an increased
* refcount.
* - FGP_FOR_MMAP: Similar to FGP_CREAT, only we want to allow the caller to do
* its own locking dance if the page is already in cache, or unlock the page
* before returning if we had to add the page to pagecache.
*
* If FGP_LOCK or FGP_CREAT are specified then the function may sleep even
* if the GFP flags specified for FGP_CREAT are atomic.
@ -1641,7 +1644,7 @@ no_page:
if (!page)
return NULL;
if (WARN_ON_ONCE(!(fgp_flags & FGP_LOCK)))
if (WARN_ON_ONCE(!(fgp_flags & (FGP_LOCK | FGP_FOR_MMAP))))
fgp_flags |= FGP_LOCK;
/* Init accessed so avoid atomic mark_page_accessed later */
@ -1655,6 +1658,13 @@ no_page:
if (err == -EEXIST)
goto repeat;
}
/*
* add_to_page_cache_lru locks the page, and for mmap we expect
* an unlocked page.
*/
if (page && (fgp_flags & FGP_FOR_MMAP))
unlock_page(page);
}
return page;
@ -2379,64 +2389,98 @@ out:
EXPORT_SYMBOL(generic_file_read_iter);
#ifdef CONFIG_MMU
/**
* page_cache_read - adds requested page to the page cache if not already there
* @file: file to read
* @offset: page index
* @gfp_mask: memory allocation flags
*
* This adds the requested page to the page cache if it isn't already there,
* and schedules an I/O to read in its contents from disk.
*
* Return: %0 on success, negative error code otherwise.
*/
static int page_cache_read(struct file *file, pgoff_t offset, gfp_t gfp_mask)
#define MMAP_LOTSAMISS (100)
static struct file *maybe_unlock_mmap_for_io(struct vm_fault *vmf,
struct file *fpin)
{
struct address_space *mapping = file->f_mapping;
struct page *page;
int ret;
int flags = vmf->flags;
do {
page = __page_cache_alloc(gfp_mask);
if (!page)
return -ENOMEM;
if (fpin)
return fpin;
ret = add_to_page_cache_lru(page, mapping, offset, gfp_mask);
if (ret == 0)
ret = mapping->a_ops->readpage(file, page);
else if (ret == -EEXIST)
ret = 0; /* losing race to add is OK */
put_page(page);
} while (ret == AOP_TRUNCATED_PAGE);
return ret;
/*
* FAULT_FLAG_RETRY_NOWAIT means we don't want to wait on page locks or
* anything, so we only pin the file and drop the mmap_sem if only
* FAULT_FLAG_ALLOW_RETRY is set.
*/
if ((flags & (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT)) ==
FAULT_FLAG_ALLOW_RETRY) {
fpin = get_file(vmf->vma->vm_file);
up_read(&vmf->vma->vm_mm->mmap_sem);
}
return fpin;
}
/*
* lock_page_maybe_drop_mmap - lock the page, possibly dropping the mmap_sem
* @vmf - the vm_fault for this fault.
* @page - the page to lock.
* @fpin - the pointer to the file we may pin (or is already pinned).
*
* This works similar to lock_page_or_retry in that it can drop the mmap_sem.
* It differs in that it actually returns the page locked if it returns 1 and 0
* if it couldn't lock the page. If we did have to drop the mmap_sem then fpin
* will point to the pinned file and needs to be fput()'ed at a later point.
*/
static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
struct file **fpin)
{
if (trylock_page(page))
return 1;
/*
* NOTE! This will make us return with VM_FAULT_RETRY, but with
* the mmap_sem still held. That's how FAULT_FLAG_RETRY_NOWAIT
* is supposed to work. We have way too many special cases..
*/
if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
return 0;
*fpin = maybe_unlock_mmap_for_io(vmf, *fpin);
if (vmf->flags & FAULT_FLAG_KILLABLE) {
if (__lock_page_killable(page)) {
/*
* We didn't have the right flags to drop the mmap_sem,
* but all fault_handlers only check for fatal signals
* if we return VM_FAULT_RETRY, so we need to drop the
* mmap_sem here and return 0 if we don't have a fpin.
*/
if (*fpin == NULL)
up_read(&vmf->vma->vm_mm->mmap_sem);
return 0;
}
} else
__lock_page(page);
return 1;
}
#define MMAP_LOTSAMISS (100)
/*
* Synchronous readahead happens when we don't even find
* a page in the page cache at all.
* Synchronous readahead happens when we don't even find a page in the page
* cache at all. We don't want to perform IO under the mmap sem, so if we have
* to drop the mmap sem we return the file that was pinned in order for us to do
* that. If we didn't pin a file then we return NULL. The file that is
* returned needs to be fput()'ed when we're done with it.
*/
static void do_sync_mmap_readahead(struct vm_fault *vmf)
static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
{
struct file *file = vmf->vma->vm_file;
struct file_ra_state *ra = &file->f_ra;
struct address_space *mapping = file->f_mapping;
struct file *fpin = NULL;
pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */
if (vmf->vma->vm_flags & VM_RAND_READ)
return;
return fpin;
if (!ra->ra_pages)
return;
return fpin;
if (vmf->vma->vm_flags & VM_SEQ_READ) {
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
page_cache_sync_readahead(mapping, ra, file, offset,
ra->ra_pages);
return;
return fpin;
}
/* Avoid banging the cache line if not needed */
@ -2448,37 +2492,44 @@ static void do_sync_mmap_readahead(struct vm_fault *vmf)
* stop bothering with read-ahead. It will only hurt.
*/
if (ra->mmap_miss > MMAP_LOTSAMISS)
return;
return fpin;
/*
* mmap read-around
*/
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
ra->start = max_t(long, 0, offset - ra->ra_pages / 2);
ra->size = ra->ra_pages;
ra->async_size = ra->ra_pages / 4;
ra_submit(ra, mapping, file);
return fpin;
}
/*
* Asynchronous readahead happens when we find the page and PG_readahead,
* so we want to possibly extend the readahead further..
* so we want to possibly extend the readahead further. We return the file that
* was pinned if we have to drop the mmap_sem in order to do IO.
*/
static void do_async_mmap_readahead(struct vm_fault *vmf,
struct page *page)
static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
struct page *page)
{
struct file *file = vmf->vma->vm_file;
struct file_ra_state *ra = &file->f_ra;
struct address_space *mapping = file->f_mapping;
struct file *fpin = NULL;
pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */
if (vmf->vma->vm_flags & VM_RAND_READ)
return;
return fpin;
if (ra->mmap_miss > 0)
ra->mmap_miss--;
if (PageReadahead(page))
if (PageReadahead(page)) {
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
page_cache_async_readahead(mapping, ra, file,
page, offset, ra->ra_pages);
}
return fpin;
}
/**
@ -2510,6 +2561,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
{
int error;
struct file *file = vmf->vma->vm_file;
struct file *fpin = NULL;
struct address_space *mapping = file->f_mapping;
struct file_ra_state *ra = &file->f_ra;
struct inode *inode = mapping->host;
@ -2531,23 +2583,26 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
* We found the page, so try async readahead before
* waiting for the lock.
*/
do_async_mmap_readahead(vmf, page);
fpin = do_async_mmap_readahead(vmf, page);
} else if (!page) {
/* No page in the page cache at all */
do_sync_mmap_readahead(vmf);
count_vm_event(PGMAJFAULT);
count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT);
ret = VM_FAULT_MAJOR;
fpin = do_sync_mmap_readahead(vmf);
retry_find:
page = find_get_page(mapping, offset);
if (!page)
goto no_cached_page;
page = pagecache_get_page(mapping, offset,
FGP_CREAT|FGP_FOR_MMAP,
vmf->gfp_mask);
if (!page) {
if (fpin)
goto out_retry;
return vmf_error(-ENOMEM);
}
}
if (!lock_page_or_retry(page, vmf->vma->vm_mm, vmf->flags)) {
put_page(page);
return ret | VM_FAULT_RETRY;
}
if (!lock_page_maybe_drop_mmap(vmf, page, &fpin))
goto out_retry;
/* Did it get truncated? */
if (unlikely(page->mapping != mapping)) {
@ -2564,6 +2619,16 @@ retry_find:
if (unlikely(!PageUptodate(page)))
goto page_not_uptodate;
/*
* We've made it this far and we had to drop our mmap_sem, now is the
* time to return to the upper layer and have it re-find the vma and
* redo the fault.
*/
if (fpin) {
unlock_page(page);
goto out_retry;
}
/*
* Found the page and have a reference on it.
* We must recheck i_size under page lock.
@ -2578,28 +2643,6 @@ retry_find:
vmf->page = page;
return ret | VM_FAULT_LOCKED;
no_cached_page:
/*
* We're only likely to ever get here if MADV_RANDOM is in
* effect.
*/
error = page_cache_read(file, offset, vmf->gfp_mask);
/*
* The page we want has now been added to the page cache.
* In the unlikely event that someone removed it in the
* meantime, we'll just come back here and read it again.
*/
if (error >= 0)
goto retry_find;
/*
* An error return from page_cache_read can result if the
* system is low on memory, or a problem occurs while trying
* to schedule I/O.
*/
return vmf_error(error);
page_not_uptodate:
/*
* Umm, take care of errors if the page isn't up-to-date.
@ -2608,12 +2651,15 @@ page_not_uptodate:
* and we need to check for errors.
*/
ClearPageError(page);
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
error = mapping->a_ops->readpage(file, page);
if (!error) {
wait_on_page_locked(page);
if (!PageUptodate(page))
error = -EIO;
}
if (fpin)
goto out_retry;
put_page(page);
if (!error || error == AOP_TRUNCATED_PAGE)
@ -2622,6 +2668,18 @@ page_not_uptodate:
/* Things didn't work out. Return zero to tell the mm layer so. */
shrink_readahead_size_eio(file, ra);
return VM_FAULT_SIGBUS;
out_retry:
/*
* We dropped the mmap_sem, we need to return to the fault handler to
* re-find the vma and come back and find our hopefully still populated
* page.
*/
if (page)
put_page(page);
if (fpin)
fput(fpin);
return ret | VM_FAULT_RETRY;
}
EXPORT_SYMBOL(filemap_fault);