On Tue, 20 Oct 2015 16:21:09 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote: > > I reviewed THP refcount redesign patch and It seems below patch fixes > MADV_FREE problem. It works well for hours. > > >From 104a0940b4c0f97e61de9fee0fd602926ff28312 Mon Sep 17 00:00:00 2001 > From: Minchan Kim <minchan@xxxxxxxxxx> > Date: Tue, 20 Oct 2015 16:00:52 +0900 > Subject: [PATCH] mm: mark head page dirty in split_huge_page > > In thp split in old THP refcount, we mappped all of pages > (ie, head + tails) to pte_mkdirty and mark PG_flags to every > tail pages. > > But with THP refcount redesign, we can lose dirty bit in page table > and PG_dirty for head page if we want to free the THP page using > migration_entry. > > It ends up discarding head page by madvise_free suddenly. > This patch fixes it by mark the head page PG_dirty when VM splits > the THP page. > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > --- > mm/huge_memory.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index adccfb48ce57..7fbbd42554a1 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3258,6 +3258,7 @@ static void __split_huge_page(struct page *page, struct list_head *list) > atomic_sub(tail_mapcount, &head->_count); > > ClearPageCompound(head); > + SetPageDirty(head); > spin_unlock_irq(&zone->lru_lock); > > unfreeze_page(page_anon_vma(head), head); This appears to be a bugfix against Kirill's "thp: reintroduce split_huge_page()"? Yes, __split_huge_page() is marking the tail pages dirty but forgot about the head page You say "we can lose dirty bit in page table" but I don't see how the above patch fixes that? Why does __split_huge_page() unconditionally mark the pages dirty, btw? Is it because the THP page was known to be dirty? If so, the head page already had PG_dirty, so this patch doesn't do anything. freeze_page(), unfreeze_page() and their callees desperately need some description of what they're doing. Kirill, could you cook somethnig up please? -- 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>