[3.13.y-ckt stable] Patch "arm64: readahead: fault retry breaks mmap file read random detection" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    arm64: readahead: fault retry breaks mmap file read random detection

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt30.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 996052251a920d4731b023608e6452496869f086 Mon Sep 17 00:00:00 2001
From: Mark Salyzyn <salyzyn at android.com>
Date: Mon, 21 Sep 2015 21:39:50 +0100
Subject: arm64: readahead: fault retry breaks mmap file read random detection

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 at kernel.org>
Cc: Rik van Riel <riel at redhat.com>
Cc: Wu Fengguang <fengguang.wu at intel.com>
Signed-off-by: Mark Salyzyn <salyzyn at android.com>
Signed-off-by: Riley Andrews <riandrews at android.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.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 c23751b..cc083b6 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -278,6 +278,7 @@ retry:
 			 * starvation.
 			 */
 			mm_flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			mm_flags |= FAULT_FLAG_TRIED;
 			goto retry;
 		}
 	}
--
1.9.1