linux-kernel - [PATCH 3.19.y-ckt 061/155] arm64: readahead: fault retry breaks mmap file read random detection

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Date:	Thu, 12 Nov 2015 15:16:55 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Shaohua Li <shli@...nel.org>, Rik van Riel <riel@...hat.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Mark Salyzyn <salyzyn@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Will Deacon <will.deacon@....com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 061/155] arm64: readahead: fault retry breaks mmap file read random detection

3.19.8-ckt10 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Salyzyn <salyzyn@...roid.com>

commit 569ba74a7ba69f46ce2950bf085b37fea2408385 upstream.

This is the arm64 portion of commit 45cac65b0fcd ("readahead: fault
retry breaks mmap file read random detection"), which was absent from
the initial port and has since gone unnoticed. The original commit says:

> .fault now can retry.  The retry can break state machine of .fault.  In
> filemap_fault, if page is miss, ra->mmap_miss is increased.  In the second
> try, since the page is in page cache now, ra->mmap_miss is decreased.  And
> these are done in one fault, so we can't detect random mmap file access.
>
> Add a new flag to indicate .fault is tried once.  In the second try, skip
> ra->mmap_miss decreasing.  The filemap_fault state machine is ok with it.

With this change, Mark reports that:

> Random read improves by 250%, sequential read improves by 40%, and
> random write by 400% to an eMMC device with dm crypto wrapped around it.

Cc: Shaohua Li <shli@...nel.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Wu Fengguang <fengguang.wu@...el.com>
Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
Signed-off-by: Riley Andrews <riandrews@...roid.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/arm64/mm/fault.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index c11cd27..44422df 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -279,6 +279,7 @@ retry:
 			 * starvation.
 			 */
 			mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			mm_flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}
-- 
1.9.1

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