linux-kernel - [PATCH 2/2] proc: meminfo: estimate available memory more conservatively

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Date:	Mon, 30 Nov 2015 15:00:22 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] proc: meminfo: estimate available memory more conservatively

The MemAvailable item in /proc/meminfo is to give users a hint of how
much memory is allocatable without causing swapping, so it excludes
the zones' low watermarks as unavailable to userspace.

However, for a userspace allocation, kswapd will actually reclaim
until the free pages hit a combination of the high watermark and the
page allocator's lowmem protection that keeps a certain amount of DMA
and DMA32 memory from userspace as well.

Subtract the full amount we know to be unavailable to userspace from
the number of free pages when calculating MemAvailable.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 fs/proc/meminfo.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index 9155a5a..df4661a 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -57,11 +57,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 	/*
 	 * Estimate the amount of memory available for userspace allocations,
 	 * without causing swapping.
-	 *
-	 * Free memory cannot be taken below the low watermark, before the
-	 * system starts swapping.
 	 */
-	available = i.freeram - wmark_low;
+	available = i.freeram - totalreserve_pages;

 	/*
 	 * Not all the page cache can be freed, otherwise the system will
-- 
2.6.2

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