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
