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

[zhouxianrong <zhouxianrong@huawei.com>]

On 2017/3/9 15:58, Vlastimil Babka wrote:
> On 03/09/2017 12:55 AM, akpm@linux-foundation.org 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
>>
>> Before you just go and hit "reply", please:
>>    a) Consider who else should be cc'ed
>>    b) Prefer to cc a suitable mailing list as well
>>    c) Ideally: find the original patch on the mailing list and do a
>>       reply-to-all to that, adding suitable additional cc's
>>
>> *** Remember to use Documentation/SubmitChecklist when testing your code ***
>>
>> The -mm tree is included into linux-next and is updated
>> there every 3-4 working days
>>
>> ------------------------------------------------------
>> From: zhouxianrong <zhouxianrong@huawei.com>
>> 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@huawei.com
>> Signed-off-by: zhouxianrong <zhouxianrong@huawei.com>
>> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Minchan Kim <minchan@kernel.org>
>> Cc: Mel Gorman <mgorman@techsingularity.net>
>> Cc: Vlastimil Babka <vbabka@suse.cz>
>> Cc: Al Viro <viro@zeniv.linux.org.uk>
>> Cc: <Mi.Sophia.Wang@huawei.com>
>> Cc: <zhouxiyu@huawei.com>
>> Cc: <weidu.du@huawei.com>
>> Cc: <zhangshiming5@huawei.com>
>> Cc: <won.ho.park@huawei.com>
>> Cc: <zhouxiaoyan1@huawei.com>
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> ---
>>
>>  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@huawei.com are
>>
>> compaction-add-def_blk_aops-migrate-function-for-memory-compaction.patch
>>
>
>
> .
>