From bde05d1ccd512696b09db9dd2e5f33ad19152605 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Tue, 29 May 2012 15:06:38 -0700 Subject: shmem: replace page if mapping excludes its zone The GMA500 GPU driver uses GEM shmem objects, but with a new twist: the backing RAM has to be below 4GB. Not a problem while the boards supported only 4GB: but now Intel's D2700MUD boards support 8GB, and their GMA3600 is managed by the GMA500 driver. shmem/tmpfs has never pretended to support hardware restrictions on the backing memory, but it might have appeared to do so before v3.1, and even now it works fine until a page is swapped out then back in. When read_cache_page_gfp() supplied a freshly allocated page for copy, that compensated for whatever choice might have been made by earlier swapin readahead; but swapoff was likely to destroy the illusion. We'd like to continue to support GMA500, so now add a new shmem_should_replace_page() check on the zone when about to move a page from swapcache to filecache (in swapin and swapoff cases), with shmem_replace_page() to allocate and substitute a suitable page (given gma500/gem.c's mapping_set_gfp_mask GFP_KERNEL | __GFP_DMA32). This does involve a minor extension to mem_cgroup_replace_page_cache() (the page may or may not have already been charged); and I've removed a comment and call to mem_cgroup_uncharge_cache_page(), which in fact is always a no-op while PageSwapCache. Also removed optimization of an unlikely path in shmem_getpage_gfp(), now that we need to check PageSwapCache more carefully (a racing caller might already have made the copy). And at one point shmem_unuse_inode() needs to use the hitherto private page_swapcount(), to guard against racing with inode eviction. It would make sense to extend shmem_should_replace_page(), to cover cpuset and NUMA mempolicy restrictions too, but set that aside for now: needs a cleanup of shmem mempolicy handling, and more testing, and ought to handle swap faults in do_swap_page() as well as shmem. Signed-off-by: Hugh Dickins Cc: Christoph Hellwig Acked-by: KAMEZAWA Hiroyuki Cc: Alan Cox Cc: Stephane Marchesin Cc: Andi Kleen Cc: Dave Airlie Cc: Daniel Vetter Cc: Rob Clark Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4f71219cc53e..d7ce417cae7c 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3373,7 +3373,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *memcg, void mem_cgroup_replace_page_cache(struct page *oldpage, struct page *newpage) { - struct mem_cgroup *memcg; + struct mem_cgroup *memcg = NULL; struct page_cgroup *pc; enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE; @@ -3383,11 +3383,20 @@ void mem_cgroup_replace_page_cache(struct page *oldpage, pc = lookup_page_cgroup(oldpage); /* fix accounting on old pages */ lock_page_cgroup(pc); - memcg = pc->mem_cgroup; - mem_cgroup_charge_statistics(memcg, false, -1); - ClearPageCgroupUsed(pc); + if (PageCgroupUsed(pc)) { + memcg = pc->mem_cgroup; + mem_cgroup_charge_statistics(memcg, false, -1); + ClearPageCgroupUsed(pc); + } unlock_page_cgroup(pc); + /* + * When called from shmem_replace_page(), in some cases the + * oldpage has already been charged, and in some cases not. + */ + if (!memcg) + return; + if (PageSwapBacked(oldpage)) type = MEM_CGROUP_CHARGE_TYPE_SHMEM; -- cgit v1.2.3-55-g7522