Convert shmem_getpage_gfp(), the engine-room of shmem, to expect
page or swap entry returned from radix tree by find_lock_page().
Whereas the repetitive old method proceeded mainly under info->lock,
dropping and repeating whenever one of the conditions needed was not
met, now we can proceed without it, leaving shmem_add_to_page_cache()
to check for a race.
This way there is no need to preallocate a page, no need for an early
radix_tree_preload(), no need for mem_cgroup_shmem_charge_fallback().
Move the error unwinding down to the bottom instead of repeating it
throughout. ENOSPC handling is a little different from before: there
is no longer any race between find_lock_page() and finding swap, but
we can arrive at ENOSPC before calling shmem_recalc_inode(), which
might occasionally discover freed space.
Be stricter to check i_size before returning. info->lock is used
for little but alloced, swapped, i_blocks updates. Move i_blocks
updates out from under the max_blocks check, so even an unlimited
size=0 mount can show accurate du.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/shmem.c | 259 ++++++++++++++++++++++-----------------------------
1 file changed, 112 insertions(+), 147 deletions(-)
--- linux.orig/mm/shmem.c 2011-06-13 13:29:44.087175010 -0700
+++ linux/mm/shmem.c 2011-06-13 13:29:55.115229689 -0700
@@ -166,15 +166,6 @@ static struct backing_dev_info shmem_bac
static LIST_HEAD(shmem_swaplist);
static DEFINE_MUTEX(shmem_swaplist_mutex);
-static void shmem_free_blocks(struct inode *inode, long pages)
-{
- struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
- if (sbinfo->max_blocks) {
- percpu_counter_add(&sbinfo->used_blocks, -pages);
- inode->i_blocks -= pages*BLOCKS_PER_PAGE;
- }
-}
-
static int shmem_reserve_inode(struct super_block *sb)
{
struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
@@ -219,9 +210,12 @@ static void shmem_recalc_inode(struct in
freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
if (freed > 0) {
+ struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
+ if (sbinfo->max_blocks)
+ percpu_counter_add(&sbinfo->used_blocks, -freed);
info->alloced -= freed;
+ inode->i_blocks -= freed * BLOCKS_PER_PAGE;
shmem_unacct_blocks(info->flags, freed);
- shmem_free_blocks(inode, freed);
}
}
@@ -888,205 +882,180 @@ static int shmem_getpage_gfp(struct inod
struct page **pagep, enum sgp_type sgp, gfp_t gfp, int *fault_type)
{
struct address_space *mapping = inode->i_mapping;
- struct shmem_inode_info *info = SHMEM_I(inode);
+ struct shmem_inode_info *info;
struct shmem_sb_info *sbinfo;
struct page *page;
- struct page *prealloc_page = NULL;
swp_entry_t swap;
int error;
+ int once = 0;
if (index > (MAX_LFS_FILESIZE >> PAGE_CACHE_SHIFT))
return -EFBIG;
repeat:
+ swap.val = 0;
page = find_lock_page(mapping, index);
- if (page) {
+ if (radix_tree_exceptional_entry(page)) {
+ swap = radix_to_swp_entry(page);
+ page = NULL;
+ }
+
+ if (sgp != SGP_WRITE &&
+ ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
+ error = -EINVAL;
+ goto failed;
+ }
+
+ if (page || (sgp == SGP_READ && !swap.val)) {
/*
* Once we can get the page lock, it must be uptodate:
* if there were an error in reading back from swap,
* the page would not be inserted into the filecache.
*/
- BUG_ON(!PageUptodate(page));
- goto done;
+ BUG_ON(page && !PageUptodate(page));
+ *pagep = page;
+ return 0;
}
/*
- * Try to preload while we can wait, to not make a habit of
- * draining atomic reserves; but don't latch on to this cpu.
+ * Fast cache lookup did not find it:
+ * bring it back from swap or allocate.
*/
- error = radix_tree_preload(gfp & GFP_RECLAIM_MASK);
- if (error)
- goto out;
- radix_tree_preload_end();
-
- if (sgp != SGP_READ && !prealloc_page) {
- prealloc_page = shmem_alloc_page(gfp, info, index);
- if (prealloc_page) {
- SetPageSwapBacked(prealloc_page);
- if (mem_cgroup_cache_charge(prealloc_page,
- current->mm, GFP_KERNEL)) {
- page_cache_release(prealloc_page);
- prealloc_page = NULL;
- }
- }
- }
+ info = SHMEM_I(inode);
+ sbinfo = SHMEM_SB(inode->i_sb);
- spin_lock(&info->lock);
- shmem_recalc_inode(inode);
- swap = shmem_get_swap(info, index);
if (swap.val) {
/* Look it up and read it in.. */
page = lookup_swap_cache(swap);
if (!page) {
- spin_unlock(&info->lock);
/* here we actually do the io */
if (fault_type)
*fault_type |= VM_FAULT_MAJOR;
page = shmem_swapin(swap, gfp, info, index);
if (!page) {
- swp_entry_t nswap = shmem_get_swap(info, index);
- if (nswap.val == swap.val) {
- error = -ENOMEM;
- goto out;
- }
- goto repeat;
+ error = -ENOMEM;
+ goto failed;
}
- wait_on_page_locked(page);
- page_cache_release(page);
- goto repeat;
}
/* We have to do this with page locked to prevent races */
- if (!trylock_page(page)) {
- spin_unlock(&info->lock);
- wait_on_page_locked(page);
- page_cache_release(page);
- goto repeat;
- }
- if (PageWriteback(page)) {
- spin_unlock(&info->lock);
- wait_on_page_writeback(page);
- unlock_page(page);
- page_cache_release(page);
- goto repeat;
- }
+ lock_page(page);
if (!PageUptodate(page)) {
- spin_unlock(&info->lock);
- unlock_page(page);
- page_cache_release(page);
error = -EIO;
- goto out;
+ goto failed;
}
+ wait_on_page_writeback(page);
- error = add_to_page_cache_locked(page, mapping,
- index, GFP_NOWAIT);
- if (error) {
- spin_unlock(&info->lock);
- if (error == -ENOMEM) {
- /*
- * reclaim from proper memory cgroup and
- * call memcg's OOM if needed.
- */
- error = mem_cgroup_shmem_charge_fallback(
- page, current->mm, gfp);
- if (error) {
- unlock_page(page);
- page_cache_release(page);
- goto out;
- }
- }
- unlock_page(page);
- page_cache_release(page);
- goto repeat;
+ /* Someone may have already done it for us */
+ if (page->mapping) {
+ if (page->mapping == mapping &&
+ page->index == index)
+ goto done;
+ error = -EEXIST;
+ goto failed;
}
- delete_from_swap_cache(page);
- shmem_put_swap(info, index, (swp_entry_t){0});
+ error = shmem_add_to_page_cache(page, mapping, index,
+ gfp, swp_to_radix_entry(swap));
+ if (error)
+ goto failed;
+
+ spin_lock(&info->lock);
info->swapped--;
+ shmem_recalc_inode(inode);
spin_unlock(&info->lock);
+
+ delete_from_swap_cache(page);
set_page_dirty(page);
swap_free(swap);
- } else if (sgp == SGP_READ) {
- page = find_get_page(mapping, index);
- if (page && !trylock_page(page)) {
- spin_unlock(&info->lock);
- wait_on_page_locked(page);
- page_cache_release(page);
- goto repeat;
+ } else {
+ if (shmem_acct_block(info->flags)) {
+ error = -ENOSPC;
+ goto failed;
}
- spin_unlock(&info->lock);
-
- } else if (prealloc_page) {
- sbinfo = SHMEM_SB(inode->i_sb);
if (sbinfo->max_blocks) {
if (percpu_counter_compare(&sbinfo->used_blocks,
- sbinfo->max_blocks) >= 0 ||
- shmem_acct_block(info->flags))
- goto nospace;
+ sbinfo->max_blocks) >= 0) {
+ error = -ENOSPC;
+ goto unacct;
+ }
percpu_counter_inc(&sbinfo->used_blocks);
- inode->i_blocks += BLOCKS_PER_PAGE;
- } else if (shmem_acct_block(info->flags))
- goto nospace;
-
- page = prealloc_page;
- prealloc_page = NULL;
-
- swap = shmem_get_swap(info, index);
- if (swap.val)
- mem_cgroup_uncharge_cache_page(page);
- else
- error = add_to_page_cache_lru(page, mapping,
- index, GFP_NOWAIT);
- /*
- * At add_to_page_cache_lru() failure,
- * uncharge will be done automatically.
- */
- if (swap.val || error) {
- shmem_unacct_blocks(info->flags, 1);
- shmem_free_blocks(inode, 1);
- spin_unlock(&info->lock);
- page_cache_release(page);
- goto repeat;
}
+ page = shmem_alloc_page(gfp, info, index);
+ if (!page) {
+ error = -ENOMEM;
+ goto decused;
+ }
+
+ SetPageSwapBacked(page);
+ __set_page_locked(page);
+ error = shmem_add_to_page_cache(page, mapping, index,
+ gfp, NULL);
+ if (error)
+ goto decused;
+ lru_cache_add_anon(page);
+
+ spin_lock(&info->lock);
info->alloced++;
+ inode->i_blocks += BLOCKS_PER_PAGE;
+ shmem_recalc_inode(inode);
spin_unlock(&info->lock);
+
clear_highpage(page);
flush_dcache_page(page);
SetPageUptodate(page);
if (sgp == SGP_DIRTY)
set_page_dirty(page);
-
- } else {
- spin_unlock(&info->lock);
- error = -ENOMEM;
- goto out;
}
done:
- *pagep = page;
- error = 0;
-out:
- if (prealloc_page) {
- mem_cgroup_uncharge_cache_page(prealloc_page);
- page_cache_release(prealloc_page);
+ /* Perhaps the file has been truncated since we checked */
+ if (sgp != SGP_WRITE &&
+ ((loff_t)index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
+ error = -EINVAL;
+ goto trunc;
}
- return error;
+ *pagep = page;
+ return 0;
-nospace:
/*
- * Perhaps the page was brought in from swap between find_lock_page
- * and taking info->lock? We allow for that at add_to_page_cache_lru,
- * but must also avoid reporting a spurious ENOSPC while working on a
- * full tmpfs.
+ * Error recovery.
*/
- page = find_get_page(mapping, index);
+trunc:
+ ClearPageDirty(page);
+ delete_from_page_cache(page);
+ spin_lock(&info->lock);
+ info->alloced--;
+ inode->i_blocks -= BLOCKS_PER_PAGE;
spin_unlock(&info->lock);
+decused:
+ if (sbinfo->max_blocks)
+ percpu_counter_add(&sbinfo->used_blocks, -1);
+unacct:
+ shmem_unacct_blocks(info->flags, 1);
+failed:
+ if (swap.val && error != -EINVAL) {
+ struct page *test = find_get_page(mapping, index);
+ if (test && !radix_tree_exceptional_entry(test))
+ page_cache_release(test);
+ /* Have another try if the entry has changed */
+ if (test != swp_to_radix_entry(swap))
+ error = -EEXIST;
+ }
if (page) {
+ unlock_page(page);
page_cache_release(page);
+ }
+ if (error == -ENOSPC && !once++) {
+ info = SHMEM_I(inode);
+ spin_lock(&info->lock);
+ shmem_recalc_inode(inode);
+ spin_unlock(&info->lock);
goto repeat;
}
- error = -ENOSPC;
- goto out;
+ if (error == -EEXIST)
+ goto repeat;
+ return error;
}
static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
@@ -1095,9 +1064,6 @@ static int shmem_fault(struct vm_area_st
int error;
int ret = VM_FAULT_LOCKED;
- if (((loff_t)vmf->pgoff << PAGE_CACHE_SHIFT) >= i_size_read(inode))
- return VM_FAULT_SIGBUS;
-
error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
if (error)
return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
@@ -2164,8 +2130,7 @@ static int shmem_remount_fs(struct super
if (config.max_inodes < inodes)
goto out;
/*
- * Those tests also disallow limited->unlimited while any are in
- * use, so i_blocks will always be zero when max_blocks is zero;
+ * Those tests disallow limited->unlimited while any are in use;
* but we must separately disallow unlimited->limited, because
* in that case we have no record of how much is already in use.
*/
--
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