From: Mel Gorman <mgorman@suse.de>
To: Michal Hocko <mhocko@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Johannes Weiner <hannes@cmpxchg.org>,
Rik van Riel <riel@redhat.com>, Neil Brown <neilb@suse.de>,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
Sage Weil <sage@inktank.com>, Mark Fasheh <mfasheh@suse.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: Use GFP_KERNEL allocation for the page cache in page_cache_read
Date: Wed, 18 Mar 2015 14:38:47 +0000 [thread overview]
Message-ID: <20150318143847.GC3087@suse.de> (raw)
In-Reply-To: <1426687766-518-1-git-send-email-mhocko@suse.cz>
On Wed, Mar 18, 2015 at 03:09:26PM +0100, Michal Hocko wrote:
> page_cache_read has been historically using page_cache_alloc_cold to
> allocate a new page. This means that mapping_gfp_mask is used as the
> base for the gfp_mask. Many filesystems are setting this mask to
> GFP_NOFS to prevent from fs recursion issues. page_cache_read is,
> however, not called from the fs layer so it doesn't need this
> protection. Even ceph and ocfs2 which call filemap_fault from their
> fault handlers seem to be OK because they are not taking any fs lock
> before invoking generic implementation.
>
> The protection might be even harmful. There is a strong push to fail
> GFP_NOFS allocations rather than loop within allocator indefinitely with
> a very limited reclaim ability. Once we start failing those requests
> the OOM killer might be triggered prematurely because the page cache
> allocation failure is propagated up the page fault path and end up in
> pagefault_out_of_memory.
>
> Use GFP_KERNEL mask instead because it is safe from the reclaim
> recursion POV. We are already doing GFP_KERNEL allocations down
> add_to_page_cache_lru path.
>
> Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: Michal Hocko <mhocko@suse.cz>
I'm very far behind after LSF/MM so do not know where this came out of
but it loses addressing restriction hints from the driver such as
drivers/gpu/drm/gma500/gem.c: mapping_set_gfp_mask(r->gem.filp->f_mapping, GFP_KERNEL | __GFP_DMA32);
It also loses mobility hints for fragmentation avoidance.
fs/inode.c: mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
If users of mapping_set_gfp_mask are now being ignored then it should at
least trigger a once-off warning that the flags are being ignored so
it's obvious if a recursion does occur and cause problems.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2015-03-18 14:38 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-18 14:09 [PATCH] mm: Use GFP_KERNEL allocation for the page cache in page_cache_read Michal Hocko
2015-03-18 14:32 ` Rik van Riel
2015-03-18 14:37 ` Michal Hocko
2015-03-18 14:38 ` Mel Gorman [this message]
2015-03-18 14:43 ` Michal Hocko
2015-03-18 14:44 ` Rik van Riel
2015-03-18 14:55 ` Michal Hocko
2015-03-19 7:14 ` Dave Chinner
2015-03-19 11:11 ` [PATCH] mm: Use GFP_KERNEL allocation for the page cache inpage_cache_read Tetsuo Handa
2015-03-19 12:44 ` [PATCH] mm: Use GFP_KERNEL allocation for the page cache in page_cache_read Michal Hocko
2015-03-20 3:48 ` Dave Chinner
2015-03-20 13:14 ` Michal Hocko
2015-03-20 22:51 ` Dave Chinner
2015-03-23 13:02 ` Michal Hocko
2015-03-26 9:53 ` Michal Hocko
2015-03-26 21:43 ` Dave Chinner
2015-03-30 8:22 ` Michal Hocko
2015-03-31 21:46 ` Dave Chinner
2015-04-07 12:16 ` Michal Hocko
2015-03-18 15:45 ` Michal Hocko
2015-03-18 21:38 ` NeilBrown
2015-03-19 13:55 ` Michal Hocko
2015-03-19 14:27 ` Michal Hocko
2015-03-20 3:57 ` Dave Chinner
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