[PATCH] mm: shmem: enable thp migration (Re: [PATCH v1] mm: consider non-anonymous thp as unmovable page)

[Naoya Horiguchi]

Hi everyone,

On Thu, Apr 05, 2018 at 06:03:17PM +0200, Michal Hocko wrote:
> On Thu 05-04-18 18:55:51, Kirill A. Shutemov wrote:
> > On Thu, Apr 05, 2018 at 05:05:47PM +0200, Michal Hocko wrote:
> > > On Thu 05-04-18 16:40:45, Kirill A. Shutemov wrote:
> > > > On Thu, Apr 05, 2018 at 02:48:30PM +0200, Michal Hocko wrote:
> > > [...]
> > > > > RIght, I confused the two. What is the proper layer to fix that then?
> > > > > rmap_walk_file?
> > > > 
> > > > Maybe something like this? Totally untested.
> > > 
> > > This looks way too complex. Why cannot we simply split THP page cache
> > > during migration?
> > 
> > This way we unify the codepath for archictures that don't support THP
> > migration and shmem THP.
> 
> But why? There shouldn't be really nothing to prevent THP (anon or
> shemem) to be migratable. If we cannot migrate it at once we can always
> split it. So why should we add another thp specific handling all over
> the place?

If thp migration works fine for shmem, we can keep anon/shmem thp to
be migratable and we don't need any ad-hoc workaround.
So I wrote a patch to enable it.
This patch does not change any shmem specific code, so I think that
it works for file thp (not only shmem,) but I don't test it yet.

Thanks,
Naoya Horiguchi
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