Re: + compaction-add-def_blk_aops-migrate-function-for-memory-compaction.patch added to -mm tree

From: zhouxianrong
Date: Thu Mar 09 2017 - 06:52:07 EST




On 2017/3/9 15:58, Vlastimil Babka wrote:
On 03/09/2017 12:55 AM, akpm@xxxxxxxxxxxxxxxxxxxx wrote:

The patch titled
Subject: compaction: add def_blk_aops migrate function for memory compaction
has been added to the -mm tree. Its filename is
compaction-add-def_blk_aops-migrate-function-for-memory-compaction.patch

This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/compaction-add-def_blk_aops-migrate-function-for-memory-compaction.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/compaction-add-def_blk_aops-migrate-function-for-memory-compaction.patch

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------------------------------------------------------
From: zhouxianrong <zhouxianrong@xxxxxxxxxx>
Subject: compaction: add def_blk_aops migrate function for memory compaction

That's not really a mm/compaction patch, but a block layer/migration patch. I
don't know internals of those so well, so I added some CC's.

The reason for doing this is based on two factors.

1. larg file read/write operations with order 0 can fragmentize
memory rapidly.

2. when a special filesystem does not supply migratepage callback,
kernel would fallback to default function fallback_migrate_page.
but fallback_migrate_page could not migrate diry page nicely;
specially kcompactd with MIGRATE_SYNC_LIGHT could not migrate
diry pages due to this until clear_page_dirty_for_io in some
procedure. i think it is not suitable here in this scenario.
for dirty pages we should migrate it rather than skip or writeout
it in kcomapctd with MIGRATE_SYNC_LIGHT. i think this problem is
for all filesystem without migratepage not only for block device fs.

So for compaction under large file writing supply migratepage for
def_blk_aops.

Is this really safe to do? buffer_migrate_page() has some assumptions listed in
its comment (and maybe more that are not listed). Do we know it's safe to use it
for all def_blk_aops users?

I could not find out differences for different disks in block device filesystem;
they should behave consistently in block device filesystem layer.

for a page of file /dev/block/xxx, when we migrate it, i think it has no difference
just like ext4 file migration.

but i dare not to say yes. i hope more peoples give their suggestions.


Link: http://lkml.kernel.org/r/1488937915-78955-1-git-send-email-zhouxianrong@xxxxxxxxxx
Signed-off-by: zhouxianrong <zhouxianrong@xxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <Mi.Sophia.Wang@xxxxxxxxxx>
Cc: <zhouxiyu@xxxxxxxxxx>
Cc: <weidu.du@xxxxxxxxxx>
Cc: <zhangshiming5@xxxxxxxxxx>
Cc: <won.ho.park@xxxxxxxxxx>
Cc: <zhouxiaoyan1@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

fs/block_dev.c | 3 +++
1 file changed, 3 insertions(+)

diff -puN fs/block_dev.c~compaction-add-def_blk_aops-migrate-function-for-memory-compaction fs/block_dev.c
--- a/fs/block_dev.c~compaction-add-def_blk_aops-migrate-function-for-memory-compaction
+++ a/fs/block_dev.c
@@ -2064,6 +2064,9 @@ static const struct address_space_operat
.releasepage = blkdev_releasepage,
.direct_IO = blkdev_direct_IO,
.is_dirty_writeback = buffer_check_dirty_writeback,
+#ifdef CONFIG_MIGRATION
+ .migratepage = buffer_migrate_page,
+#endif
};

#define BLKDEV_FALLOC_FL_SUPPORTED \
_

Patches currently in -mm which might be from zhouxianrong@xxxxxxxxxx are

compaction-add-def_blk_aops-migrate-function-for-memory-compaction.patch



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