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mm, memcg: use consistent gfp flags during readahead

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Vladimir has noticed that we might declare memcg oom even during
readahead because read_pages only uses GFP_KERNEL (with mapping_gfp
restriction) while __do_page_cache_readahead uses
page_cache_alloc_readahead which adds __GFP_NORETRY to prevent from
OOMs.  This gfp mask discrepancy is really unfortunate and easily
fixable.  Drop page_cache_alloc_readahead() which only has one user and
outsource the gfp_mask logic into readahead_gfp_mask and propagate this
mask from __do_page_cache_readahead down to read_pages.

This alone would have only very limited impact as most filesystems are
implementing ->readpages and the common implementation mpage_readpages
does GFP_KERNEL (with mapping_gfp restriction) again.  We can tell it to
use readahead_gfp_mask instead as this function is called only during
readahead as well.  The same applies to read_cache_pages.

ext4 has its own ext4_mpage_readpages but the path which has pages !=
NULL can use the same gfp mask.  Btrfs, cifs, f2fs and orangefs are
doing a very similar pattern to mpage_readpages so the same can be
applied to them as well.

[[email protected]: coding-style fixes]
[[email protected]: restrict gfp mask in mpage_alloc]
  Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Steve French <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: Mike Marshall <[email protected]>
Cc: Jaegeuk Kim <[email protected]>
Cc: Changman Lee <[email protected]>
Cc: Chao Yu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michal Hocko 2016-07-26 15:24:53 -07:00 • committed by Linus Torvalds
commit 8a5c743e30
8 changed files with 19 additions and 16 deletions
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13
mm/readahead.c
View file

@ -89,7 +89,7 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
page = lru_to_page(pages);
list_del(&page->lru);
if (add_to_page_cache_lru(page, mapping, page->index,
mapping_gfp_constraint(mapping, GFP_KERNEL))) {
readahead_gfp_mask(mapping))) {
read_cache_pages_invalidate_page(mapping, page);
continue;
}
@ -108,7 +108,7 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages,
EXPORT_SYMBOL(read_cache_pages);
static int read_pages(struct address_space *mapping, struct file *filp,
struct list_head *pages, unsigned nr_pages)
struct list_head *pages, unsigned int nr_pages, gfp_t gfp)
{
struct blk_plug plug;
unsigned page_idx;
@ -126,10 +126,8 @@ static int read_pages(struct address_space *mapping, struct file *filp,
for (page_idx = 0; page_idx < nr_pages; page_idx++) {
struct page *page = lru_to_page(pages);
list_del(&page->lru);
if (!add_to_page_cache_lru(page, mapping, page->index,
mapping_gfp_constraint(mapping, GFP_KERNEL))) {
if (!add_to_page_cache_lru(page, mapping, page->index, gfp))
mapping->a_ops->readpage(filp, page);
}
put_page(page);
}
ret = 0;
@ -159,6 +157,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
int page_idx;
int ret = 0;
loff_t isize = i_size_read(inode);
gfp_t gfp_mask = readahead_gfp_mask(mapping);
if (isize == 0)
goto out;
@ -180,7 +179,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
if (page && !radix_tree_exceptional_entry(page))
continue;
page = page_cache_alloc_readahead(mapping);
page = __page_cache_alloc(gfp_mask);
if (!page)
break;
page->index = page_offset;
@ -196,7 +195,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
* will then handle the error.
*/
if (ret)
read_pages(mapping, filp, &page_pool, ret);
read_pages(mapping, filp, &page_pool, ret, gfp_mask);
BUG_ON(!list_empty(&page_pool));
out:
return ret;