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Commit 8a5c743e authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
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mm, memcg: use consistent gfp flags during readahead 

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.

[akpm@linux-foundation.org: coding-style fixes]
[mhocko@suse.com: restrict gfp mask in mpage_alloc]
  Link: http://lkml.kernel.org/r/20160610074223.GC32285@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/1465301556-26431-1-git-send-email-mhocko@kernel.org


Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Chris Mason <clm@fb.com>
Cc: Steve French <sfrench@samba.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Jan Kara <jack@suse.cz>
Cc: Mike Marshall <hubcap@omnibond.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Changman Lee <cm224.lee@samsung.com>
Cc: Chao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e5e3f4c4

fs/btrfs/extent_io.c

+2 −1
Original line number Diff line number Diff line
@@ -4180,7 +4180,8 @@ int extent_readpages(struct extent_io_tree *tree, 
		prefetchw(&page->flags);

		list_del(&page->lru);

		if (add_to_page_cache_lru(page, mapping,

					page->index, GFP_NOFS)) {

					page->index,

					readahead_gfp_mask(mapping))) {

			put_page(page);

			continue;

		}

fs/cifs/file.c

+1 −1
Original line number Diff line number Diff line
@@ -3366,7 +3366,7 @@ readpages_get_pages(struct address_space *mapping, struct list_head *page_list, 
	struct page *page, *tpage;

	unsigned int expected_index;

	int rc;

	gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);

	gfp_t gfp = readahead_gfp_mask(mapping);



	INIT_LIST_HEAD(tmplist);

fs/ext4/readpage.c

+1 −1
Original line number Diff line number Diff line
@@ -166,7 +166,7 @@ int ext4_mpage_readpages(struct address_space *mapping, 
			page = list_entry(pages->prev, struct page, lru);

			list_del(&page->lru);

			if (add_to_page_cache_lru(page, mapping, page->index,

				  mapping_gfp_constraint(mapping, GFP_KERNEL)))

				  readahead_gfp_mask(mapping)))

				goto next_page;

		}

fs/f2fs/data.c

+2 −1
Original line number Diff line number Diff line
@@ -996,7 +996,8 @@ static int f2fs_mpage_readpages(struct address_space *mapping, 
			page = list_entry(pages->prev, struct page, lru);

			list_del(&page->lru);

			if (add_to_page_cache_lru(page, mapping,

						  page->index, GFP_KERNEL))

						  page->index,

						  readahead_gfp_mask(mapping)))

				goto next_page;

		}

fs/mpage.c

+3 −1
Original line number Diff line number Diff line
@@ -71,6 +71,8 @@ mpage_alloc(struct block_device *bdev, 
{

	struct bio *bio;



	/* Restrict the given (page cache) mask for slab allocations */

	gfp_flags &= GFP_KERNEL;

	bio = bio_alloc(gfp_flags, nr_vecs);



	if (bio == NULL && (current->flags & PF_MEMALLOC)) {
@@ -362,7 +364,7 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages, 
	sector_t last_block_in_bio = 0;

	struct buffer_head map_bh;

	unsigned long first_logical_block = 0;

	gfp_t gfp = mapping_gfp_constraint(mapping, GFP_KERNEL);

	gfp_t gfp = readahead_gfp_mask(mapping);



	map_bh.b_state = 0;

	map_bh.b_size = 0;