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

[zhouxianrong]

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
> >
> > 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@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
>
>
> .