Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753563AbZDVFlF (ORCPT ); Wed, 22 Apr 2009 01:41:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752333AbZDVFkx (ORCPT ); Wed, 22 Apr 2009 01:40:53 -0400 Received: from TYO201.gate.nec.co.jp ([202.32.8.193]:39693 "EHLO tyo201.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752008AbZDVFkw (ORCPT ); Wed, 22 Apr 2009 01:40:52 -0400 Date: Wed, 22 Apr 2009 14:38:33 +0900 From: Daisuke Nishimura To: KAMEZAWA Hiroyuki Cc: nishimura@mxp.nes.nec.co.jp, "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "balbir@linux.vnet.ibm.com" , "hugh@veritas.com" Subject: Re: [RFC][PATCH] fix swap entries is not reclaimed in proper way for mem+swap controller Message-Id: <20090422143833.2e11e10b.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20090421162121.1a1d15fe.kamezawa.hiroyu@jp.fujitsu.com> References: <20090421162121.1a1d15fe.kamezawa.hiroyu@jp.fujitsu.com> Organization: NEC Soft, Ltd. X-Mailer: Sylpheed 2.6.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11626 Lines: 327 On Tue, 21 Apr 2009 16:21:21 +0900, KAMEZAWA Hiroyuki wrote: > maybe this patch covers almost all cases of swap-leak of memcg, Nishimura-san > reported. There are many callers of lock_page() but lock_page() which can > be racy with free_swap_and_cache() is not so much, I think. > > Nishimura-san, How about this ? > Thank you for your patch. I've run this patch last night but unfortunately I got a BUG. BUG: sleeping function called from invalid context at include/linux/pagemap.h:327 in_atomic(): 1, irqs_disabled(): 0, pid: 9230, name: page01 hmm, calling lock_page() in end_swap_bio_* seems not safe. And, some comments are inlined. > == > From: KAMEZAWA Hiroyuki > > free_swap_and_cache(), which is called under various spin_lock, > is designed to be best-effort function and it does nothing if the page > is locked, under I/O. But it's ok because global lru will find the page finally. > > But, when it comes to memory+swap cgroup, global LRU may not work and > swap entry can be alive as "not used but not freed" state for very very long time > because memory cgroup's LRU routine scans its own LRU only. > (Such stale swap-cache is out of memcg's LRU) > > Nishimura repoted such kind of swap cache makes memcg unstable and > - we can never free mem_cgroup object (....it's big) even if no users. > - OOM killer can happen because amounts of charge-to-swap is leaked. > And - All the swap space(swap entries) could be exhausted by these swap cache. > This patch tries to fix the problem by adding PageCgroupStale() flag. > If a page which is under zappped is busy swap cache, recored it as Stale. > At the end of swap I/O, Stale flag is checked and swap and swapcache is > freed if necessary. Page migration case is also checked. > > > Reported-by: Daisuke Nishimura > Signed-off-by: KAMEZAWA Hiroyuki > > --- > include/linux/page_cgroup.h | 4 +++ > include/linux/swap.h | 8 ++++++ > mm/memcontrol.c | 51 ++++++++++++++++++++++++++++++++++++++++---- > mm/page_io.c | 2 + > mm/swapfile.c | 1 > 5 files changed, 62 insertions(+), 4 deletions(-) > > Index: linux-2.6.30-rc2/include/linux/page_cgroup.h > =================================================================== > --- linux-2.6.30-rc2.orig/include/linux/page_cgroup.h > +++ linux-2.6.30-rc2/include/linux/page_cgroup.h > @@ -26,6 +26,7 @@ enum { > PCG_LOCK, /* page cgroup is locked */ > PCG_CACHE, /* charged as cache */ > PCG_USED, /* this object is in use. */ > + PCG_STALE, /* may be a stale swap-cache */ > }; > > #define TESTPCGFLAG(uname, lname) \ > @@ -46,6 +47,9 @@ TESTPCGFLAG(Cache, CACHE) > TESTPCGFLAG(Used, USED) > CLEARPCGFLAG(Used, USED) > > +TESTPCGFLAG(Stale, STALE) > +SETPCGFLAG(Stale, STALE) > + > static inline int page_cgroup_nid(struct page_cgroup *pc) > { > return page_to_nid(pc->page); > Index: linux-2.6.30-rc2/include/linux/swap.h > =================================================================== > --- linux-2.6.30-rc2.orig/include/linux/swap.h > +++ linux-2.6.30-rc2/include/linux/swap.h > @@ -344,10 +344,18 @@ mem_cgroup_uncharge_swapcache(struct pag > #endif > #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP > extern void mem_cgroup_uncharge_swap(swp_entry_t ent); > +extern void mem_cgroup_mark_swapcache_stale(struct page *page); > +extern void mem_cgroup_fixup_swapcache(struct page *page); > #else > static inline void mem_cgroup_uncharge_swap(swp_entry_t ent) > { > } > +static void mem_cgroup_check_mark_swapcache_stale(struct page *page) > +{ > +} > +static void mem_cgroup_fixup_swapcache(struct page *page) > +{ > +} > #endif > I think they should be defined in MEM_RES_CTLR case. Exhausting swap entries problem is not depend on MEM_RES_CTLR_SWAP. > #else /* CONFIG_SWAP */ > Index: linux-2.6.30-rc2/mm/memcontrol.c > =================================================================== > --- linux-2.6.30-rc2.orig/mm/memcontrol.c > +++ linux-2.6.30-rc2/mm/memcontrol.c > @@ -1534,6 +1534,47 @@ void mem_cgroup_uncharge_swap(swp_entry_ > } > rcu_read_unlock(); > } > + > +/* > + * free_swap_and_cache() is an best-effort function and it doesn't free > + * swapent if the swapcache seems to be busy (ex. the page is locked.) > + * This behavior is designed to be as is but mem+swap cgroup has to handle it. > + * Otherwise, swp_entry seems to be leaked (for very long time) > + */ > +void mem_cgroup_mark_swapcache_stale(struct page *page) > +{ > + struct page_cgroup *pc; > + > + if (!PageSwapCache(page) || page_mapped(page)) > + return; > + > + pc = lookup_page_cgroup(page); > + lock_page_cgroup(pc); > + > + /* > + * This "Stale" flag will be cleared when the page is reused > + * somewhere. > + */ > + if (!PageCgroupUsed(pc)) > + SetPageCgroupStale(pc); > + unlock_page_cgroup(pc); > +} > + > +void mem_cgroup_fixup_swapcache(struct page *page) > +{ > + struct page_cgroup *pc = lookup_page_cgroup(page); > + > + /* Stale flag will be cleared automatically */ > + if (unlikely(PageCgroupStale(pc))) { > + if (get_page_unless_zero(page)) { > + lock_page(page); > + try_to_free_swap(page); > + unlock_page(page); > + page_cache_release(page); > + } > + } > +} > + > #endif > > /* > @@ -1604,17 +1645,19 @@ void mem_cgroup_end_migration(struct mem > __mem_cgroup_commit_charge(mem, pc, ctype); > > /* > - * Both of oldpage and newpage are still under lock_page(). > - * Then, we don't have to care about race in radix-tree. > - * But we have to be careful that this page is unmapped or not. > + * oldpage is under lock_page() at migration. Then, we don't have to > + * care about race in radix-tree. But we have to be careful > + * that this page is unmapped or not. > * > * There is a case for !page_mapped(). At the start of > * migration, oldpage was mapped. But now, it's zapped. > * But we know *target* page is not freed/reused under us. > * mem_cgroup_uncharge_page() does all necessary checks. > */ > - if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED) > + if (ctype == MEM_CGROUP_CHARGE_TYPE_MAPPED) { > mem_cgroup_uncharge_page(target); > + mem_cgroup_fixup_swapcache(target); > + } > } > > /* hmm, the intention of the patch I posted(*) is not free stale SwapCache. * http://marc.info/?l=linux-mm&m=124029196025611&w=2 If the oldpage was page_mapped() and !PageSwapCache, newpage would be uncharge by mem_cgroup_uncharge_page() if the owner process has been exited (because newpage is !page_mapped()). But if the oldpage was page_mapped and PageSwapCache, newpage cannot be uncharged by mem_cgroup_uncharge_page() even if the owner process has been exited. Those SwapCache is put_back'ed to memcg's LRU, so it can be reclaimed if memcg's LRU scaning(Anon) run, but my intention was to fix this behavior for consistency. > Index: linux-2.6.30-rc2/mm/page_io.c > =================================================================== > --- linux-2.6.30-rc2.orig/mm/page_io.c > +++ linux-2.6.30-rc2/mm/page_io.c > @@ -68,6 +68,7 @@ static void end_swap_bio_write(struct bi > } > end_page_writeback(page); > bio_put(bio); > + mem_cgroup_fixup_swapcache(page); > } > > void end_swap_bio_read(struct bio *bio, int err) > @@ -87,6 +88,7 @@ void end_swap_bio_read(struct bio *bio, > } > unlock_page(page); > bio_put(bio); > + mem_cgroup_fixup_swapcache(page); > } > > /* > Index: linux-2.6.30-rc2/mm/swapfile.c > =================================================================== > --- linux-2.6.30-rc2.orig/mm/swapfile.c > +++ linux-2.6.30-rc2/mm/swapfile.c > @@ -587,6 +587,7 @@ int free_swap_and_cache(swp_entry_t entr > if (swap_entry_free(p, entry) == 1) { > page = find_get_page(&swapper_space, entry.val); > if (page && !trylock_page(page)) { > + mem_cgroup_mark_swapcache_stale(page); > page_cache_release(page); > page = NULL; > } > IIUC, this patch cannot handle(even if it worked as intended) cases like: processA | processB -------------------------------------+------------------------------------- (free_swap_and_cache()) | (read_swap_cache_async()) | swap_duplicate() swap_entry_free() == 1 | find_get_page() | -> cannot find. so | PCG_STALE isn't set. | | add_to_swap_cache() | | swap_readpage() | end_swap_bio_read() | mem_cgroup_fixup_swapcache() | does nothing becase !PageCgroupStale (the page is mapped but not on swapcache) processA | processB -------------------------------------+------------------------------------- (zap_pte_range()) | (shrink_page_list()) | (referenced flag is set in some reason) page_remove_rmap() | -> uncharged(!PageSwapCache) | | add_to_swap() | -> succeed | | (not freed because referenced flag is set) So, we should add check to shrink_page_list() anyway, IMHO. Hmm... I tested a patch like below, but it seems to have a dead lock about swap_lock. (This patch has unhandled corner cases yet, even if it worked.) I'll dig and try more including another aproach.. --- diff --git a/include/linux/swap.h b/include/linux/swap.h index 62d8143..991dd53 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -336,11 +336,16 @@ static inline void disable_swap_token(void) #ifdef CONFIG_CGROUP_MEM_RES_CTLR extern void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent); +extern void mem_cgroup_fixup_swapcache(struct page *page); #else static inline void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) { } +static inline void +mem_cgroup_fixup_swapcache(struct page *page) +{ +} #endif #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP extern void mem_cgroup_uncharge_swap(swp_entry_t ent); diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ba07cab..b2a4d52 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1568,6 +1568,19 @@ void mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent) css_put(&memcg->css); } +void mem_cgroup_fixup_swapcache(struct page *page) +{ + if (mem_cgroup_disabled()) + return; + + VM_BUG_ON(!PageLocked(page)); + + if (get_page_unless_zero(page)) { + try_to_free_swap(page); + page_cache_release(page); + } +} + #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP /* * called from swap_entry_free(). remove record in swap_cgroup and diff --git a/mm/page_io.c b/mm/page_io.c index 3023c47..2bafcd3 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -85,6 +85,7 @@ void end_swap_bio_read(struct bio *bio, int err) } else { SetPageUptodate(page); } + mem_cgroup_fixup_swapcache(page); unlock_page(page); bio_put(bio); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/