linux-kernel - [PATCH] mm, slaub: Add __GFP_ATOMIC to the GFP reclaim mask

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Message-ID: <20160610093832.GK2527@techsingularity.net>
Date:	Fri, 10 Jun 2016 10:38:32 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Marcin Wojtas <mw@...ihalf.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH] mm, slaub: Add __GFP_ATOMIC to the GFP reclaim mask

Commit d0164adc89f6 ("mm, page_alloc: distinguish between being unable to
sleep, unwilling to sleep and avoiding waking kswapd") modified __GFP_WAIT
to explicitly identify the difference between atomic callers and those that
were unwilling to sleep. Later the definition was removed entirely.

The GFP_RECLAIM_MASK is the set of flags that affect watermark checking
and reclaim behaviour but __GFP_ATOMIC was never added. Without it, atomic
users of the slab allocator strip the __GFP_ATOMIC flag and cannot access
the page allocator atomic reserves.  This patch addresses the problem.

The user-visible impact depends on the workload but potentially atomic
allocations unnecessarily fail without this path.

Cc: <stable@...r.kernel.org> # 4.4+
Reported-by: Marcin Wojtas <mw@...ihalf.com>
Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 mm/internal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/internal.h b/mm/internal.h
index a37e5b6f9d25..2524ec880e24 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -24,7 +24,8 @@
  */
 #define GFP_RECLAIM_MASK (__GFP_RECLAIM|__GFP_HIGH|__GFP_IO|__GFP_FS|\
 			__GFP_NOWARN|__GFP_REPEAT|__GFP_NOFAIL|\
-			__GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC)
+			__GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC|\
+			__GFP_ATOMIC)

 /* The GFP flags allowed during early boot */
 #define GFP_BOOT_MASK (__GFP_BITS_MASK & ~(__GFP_RECLAIM|__GFP_IO|__GFP_FS))