From 64d6519dda3905dfb94d3f93c07c5f263f41813f Mon Sep 17 00:00:00 2001 From: Lee Schermerhorn Date: Sat, 18 Oct 2008 20:26:52 -0700 Subject: swap: cull unevictable pages in fault path In the fault paths that install new anonymous pages, check whether the page is evictable or not using lru_cache_add_active_or_unevictable(). If the page is evictable, just add it to the active lru list [via the pagevec cache], else add it to the unevictable list. This "proactive" culling in the fault path mimics the handling of mlocked pages in Nick Piggin's series to keep mlocked pages off the lru lists. Notes: 1) This patch is optional--e.g., if one is concerned about the additional test in the fault path. We can defer the moving of nonreclaimable pages until when vmscan [shrink_*_list()] encounters them. Vmscan will only need to handle such pages once, but if there are a lot of them it could impact system performance. 2) The 'vma' argument to page_evictable() is require to notice that we're faulting a page into an mlock()ed vma w/o having to scan the page's rmap in the fault path. Culling mlock()ed anon pages is currently the only reason for this patch. 3) We can't cull swap pages in read_swap_cache_async() because the vma argument doesn't necessarily correspond to the swap cache offset passed in by swapin_readahead(). This could [did!] result in mlocking pages in non-VM_LOCKED vmas if [when] we tried to cull in this path. 4) Move set_pte_at() to after where we add page to lru to keep it hidden from other tasks that might walk the page table. We already do it in this order in do_anonymous() page. And, these are COW'd anon pages. Is this safe? [riel@redhat.com: undo an overzealous code cleanup] Signed-off-by: Lee Schermerhorn Signed-off-by: Rik van Riel Signed-off-by: KOSAKI Motohiro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swap.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'mm/swap.c') diff --git a/mm/swap.c b/mm/swap.c index bc58c1369dd6..2152e48a7b8f 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -31,6 +31,8 @@ #include #include +#include "internal.h" + /* How many pages do we try to swap or page in/out together? */ int page_cluster; @@ -244,6 +246,25 @@ void add_page_to_unevictable_list(struct page *page) spin_unlock_irq(&zone->lru_lock); } +/** + * lru_cache_add_active_or_unevictable + * @page: the page to be added to LRU + * @vma: vma in which page is mapped for determining reclaimability + * + * place @page on active or unevictable LRU list, depending on + * page_evictable(). Note that if the page is not evictable, + * it goes directly back onto it's zone's unevictable list. It does + * NOT use a per cpu pagevec. + */ +void lru_cache_add_active_or_unevictable(struct page *page, + struct vm_area_struct *vma) +{ + if (page_evictable(page, vma)) + lru_cache_add_lru(page, LRU_ACTIVE + page_is_file_cache(page)); + else + add_page_to_unevictable_list(page); +} + /* * Drain pages out of the cpu's pagevecs. * Either "cpu" is the current CPU, and preemption has already been -- cgit v1.2.3