Patch "arm64: readahead: fault retry breaks mmap file read random detection" has been added to the 4.2-stable tree

Patch "arm64: readahead: fault retry breaks mmap file read random detection" has been added to the 4.2-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

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

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     arm64-readahead-fault-retry-breaks-mmap-file-read-random-detection.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 569ba74a7ba69f46ce2950bf085b37fea2408385 Mon Sep 17 00:00:00 2001
From: Mark Salyzyn <salyzyn@android.com>
Date: Mon, 21 Sep 2015 21:39:50 +0100
Subject: arm64: readahead: fault retry breaks mmap file read random detection

From: Mark Salyzyn <salyzyn@android.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@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Signed-off-by: Riley Andrews <riandrews@android.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm64/mm/fault.c |    1 +
 1 file changed, 1 insertion(+)

--- 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;
 		}
 	}


Patches currently in stable-queue which might be from salyzyn@android.com are

queue-4.2/arm64-readahead-fault-retry-breaks-mmap-file-read-random-detection.patch