linux-kernel - [PATCH 31/31] huge tmpfs: no kswapd by default on sync allocations

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Date:	Tue, 5 Apr 2016 15:07:29 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andres Lagar-Cavilla <andreslc@...gle.com>,
	Yang Shi <yang.shi@...aro.org>, Ning Qu <quning@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 31/31] huge tmpfs: no kswapd by default on sync allocations

From: Andres Lagar-Cavilla <andreslc@...gle.com>

This triggers early compaction abort while in process context, to
ameliorate mmap semaphore stalls.

Suggested-by: David Rientjes <rientjes@...gle.com>
Signed-off-by: Andres Lagar-Cavilla <andreslc@...gle.com>
Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
 Documentation/filesystems/tmpfs.txt |    5 +++--
 mm/shmem.c                          |    3 ++-
 2 files changed, 5 insertions(+), 3 deletions(-)

--- a/Documentation/filesystems/tmpfs.txt
+++ b/Documentation/filesystems/tmpfs.txt
@@ -194,8 +194,9 @@ to force huge off for all (intended for
 
 /proc/sys/vm/shmem_huge_gfpmask (intended for experimentation only):
 
-Default 38146762, that is 0x24612ca:
-GFP_HIGHUSER_MOVABLE|__GFP_NOWARN|__GFP_THISNODE|__GFP_NORETRY.
+Default 4592330, that is 0x4612ca:
+GFP_HIGHUSER_MOVABLE|__GFP_NOWARN|__GFP_THISNODE|__GFP_NORETRY
+minus __GFP_KSWAPD_RECLAIM.
 Write a gfpmask built from __GFP flags in include/linux/gfp.h, to experiment
 with better alternatives for the synchronous huge tmpfs allocation used
 when faulting or writing.
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -324,7 +324,8 @@ int shmem_huge __read_mostly;
 int shmem_huge_recoveries __read_mostly = 8;	/* concurrent recovery limit */
 
 int shmem_huge_gfpmask __read_mostly =
-	(int)(GFP_HIGHUSER_MOVABLE|__GFP_NOWARN|__GFP_THISNODE|__GFP_NORETRY);
+	(int)(GFP_HIGHUSER_MOVABLE|__GFP_NOWARN|__GFP_THISNODE|__GFP_NORETRY) &
+	~__GFP_KSWAPD_RECLAIM;
 int shmem_recovery_gfpmask __read_mostly =
 	(int)(GFP_HIGHUSER_MOVABLE|__GFP_NOWARN|__GFP_THISNODE);