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SubjectRe: [PATCH v1] mm: consider non-anonymous thp as unmovable page
On Thu 05-04-18 13:58:43, Zi Yan wrote:
> On 5 Apr 2018, at 12:03, 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?
>
> Then, it would be much easier if your "unclutter thp migration" patches is merged,
> plus the patch below:

Good point. Except I would prefer a less convoluted condition

> diff --git a/mm/migrate.c b/mm/migrate.c
> index 60531108021a..b4087aa890f5 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1138,7 +1138,9 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
> int rc = MIGRATEPAGE_SUCCESS;
> struct page *newpage;
>
> - if (!thp_migration_supported() && PageTransHuge(page))
> + if ((!thp_migration_supported() ||
> + (thp_migration_supported() && !PageAnon(page))) &&
> + PageTransHuge(page))
> return -ENOMEM;

What about this?
diff --git a/mm/migrate.c b/mm/migrate.c
index 5d0dc7b85f90..cd02e2bdf37c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1138,7 +1138,11 @@ static ICE_noinline int unmap_and_move(new_page_t get_new_page,
int rc = MIGRATEPAGE_SUCCESS;
struct page *newpage;

- if (!thp_migration_supported() && PageTransHuge(page))
+ /*
+ * THP pagecache or generally non-migrateable THP need to be split
+ * up before migration
+ */
+ if (PageTransHuge(page) && (!thp_migration_supported() || !PageAnon(page)))
return -ENOMEM;

newpage = get_new_page(page, private);

--
Michal Hocko
SUSE Labs

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