On Thu, 24 Apr 2014, Mel Gorman wrote: > Migration of misplaced transhuge pages uses page_add_new_anon_rmap() when > putting the page back as it avoided an atomic operations and added the > new page to the correct LRU. A side-effect is that the page gets marked > activated as part of the migration meaning that transhuge and base pages > are treated differently from an aging perspective than base page migration. > > This patch uses page_add_anon_rmap() and putback_lru_page() on completion of > a transhuge migration similar to base page migration. It would fewer atomic > operations to use lru_cache_add without taking an additional reference to the > page. The downside would be that it's still different to base page migration > and unevictable pages may be added to the wrong LRU for cleaning up later. > Testing of the usual workloads did not show any adverse impact to the > change. > > Signed-off-by: Mel Gorman <mgorman@xxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Thanks, Mel: I do feel more comfortable doing it this way, as elsewhere in migrate.c, whatever the slight drawbacks (I hadn't realized that I was asking for another get_page, but it's far from the only place where isolate/putback forces us into that additional superfluous reference: something to sort out "some other day"). I worried for a bit that you are doing the putback while holding page lock; but this is not the only place where that's done (page_remove_rmap may clear_page_mlock though called under page lock), so no good reason to ask for a change there. > --- > mm/migrate.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index bed4880..6247be7 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1852,7 +1852,7 @@ fail_putback: > * guarantee the copy is visible before the pagetable update. > */ > flush_cache_range(vma, mmun_start, mmun_end); > - page_add_new_anon_rmap(new_page, vma, mmun_start); > + page_add_anon_rmap(new_page, vma, mmun_start); > pmdp_clear_flush(vma, mmun_start, pmd); > set_pmd_at(mm, mmun_start, pmd, entry); > flush_tlb_range(vma, mmun_start, mmun_end); > @@ -1877,6 +1877,10 @@ fail_putback: > spin_unlock(ptl); > mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end); > > + /* Take an "isolate" reference and put new page on the LRU. */ > + get_page(new_page); > + putback_lru_page(new_page); > + > unlock_page(new_page); > unlock_page(page); > put_page(page); /* Drop the rmap reference */ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>