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: Michal 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/ext4/readpage.c b/fs/ext4/readpage.c
index dc54a4b..c75b66a 100644
--- a/fs/ext4/readpage.c
+++ b/fs/ext4/readpage.c
@@ -166,7 +166,7 @@
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;
}