From 45961722f8e30ceab9d135b1ddc0947d53aef7c3 Mon Sep 17 00:00:00 2001 From: Konstantin Weitz Date: Wed, 17 Apr 2013 13:59:32 +0200 Subject: mm: add support for discard of unused ptes In a virtualized environment and given an appropriate interface the guest can mark pages as unused while they are free (for the s390 implementation see git commit 45e576b1c3d00206 "guest page hinting light"). For the host the unused state is a property of the pte. This patch adds the primitive 'pte_unused' and code to the host swap out handler so that pages marked as unused by all mappers are not swapped out but discarded instead, thus saving one IO for swap out and potentially another one for swap in. [ Martin Schwidefsky: patch reordering and simplification ] Signed-off-by: Konstantin Weitz Signed-off-by: Martin Schwidefsky --- mm/rmap.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'mm') diff --git a/mm/rmap.c b/mm/rmap.c index d9d4231..9056a1f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1165,6 +1165,16 @@ int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, } set_pte_at(mm, address, pte, swp_entry_to_pte(make_hwpoison_entry(page))); + } else if (pte_unused(pteval)) { + /* + * The guest indicated that the page content is of no + * interest anymore. Simply discard the pte, vmscan + * will take care of the rest. + */ + if (PageAnon(page)) + dec_mm_counter(mm, MM_ANONPAGES); + else + dec_mm_counter(mm, MM_FILEPAGES); } else if (PageAnon(page)) { swp_entry_t entry = { .val = page_private(page) }; pte_t swp_pte; -- cgit v1.1