Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754623AbYLOIlf (ORCPT ); Mon, 15 Dec 2008 03:41:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752227AbYLOIl1 (ORCPT ); Mon, 15 Dec 2008 03:41:27 -0500 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:44893 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752164AbYLOIl1 (ORCPT ); Mon, 15 Dec 2008 03:41:27 -0500 Date: Mon, 15 Dec 2008 17:40:28 +0900 From: KAMEZAWA Hiroyuki To: balbir@linux.vnet.ibm.com Cc: Hugh Dickins , Daisuke Nishimura , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" Subject: Re: [BUGFIX][PATCH mmotm] memcg fix swap accounting leak (v3) Message-Id: <20081215174028.8baf7739.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20081215083726.GH18403@balbir.in.ibm.com> References: <20081212172930.282caa38.kamezawa.hiroyu@jp.fujitsu.com> <20081212184341.b62903a7.nishimura@mxp.nes.nec.co.jp> <46730.10.75.179.61.1229080565.squirrel@webmail-b.css.fujitsu.com> <20081213160310.e9501cd9.kamezawa.hiroyu@jp.fujitsu.com> <4409.10.75.179.62.1229164064.squirrel@webmail-b.css.fujitsu.com> <20081215160751.b6a944be.kamezawa.hiroyu@jp.fujitsu.com> <20081215083726.GH18403@balbir.in.ibm.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 2.5.0 (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: 7670 Lines: 191 On Mon, 15 Dec 2008 14:07:26 +0530 Balbir Singh wrote: > * KAMEZAWA Hiroyuki [2008-12-15 16:07:51]: > > > > > From: KAMEZAWA Hiroyuki > > > > Fix swapin charge operation of memcg. > > > > Now, memcg has hooks to swap-out operation and checks SwapCache is really > > unused or not. That check depends on contents of struct page. > > I.e. If PageAnon(page) && page_mapped(page), the page is recoginized as > > still-in-use. > > > > Now, reuse_swap_page() calles delete_from_swap_cache() before establishment > > of any rmap. Then, in followinig sequence > > > > (Page fault with WRITE) > > try_charge() (charge += PAGESIZE) > > commit_charge() (Check page_cgroup is used or not..) > > reuse_swap_page() > > -> delete_from_swapcache() > > -> mem_cgroup_uncharge_swapcache() (charge -= PAGESIZE) > > ...... > > New charge is uncharged soon.... > > To avoid this, move commit_charge() after page_mapcount() goes up to 1. > > By this, > > > > try_charge() (usage += PAGESIZE) > > reuse_swap_page() (may usage -= PAGESIZE if PCG_USED is set) > > commit_charge() (If page_cgroup is not marked as PCG_USED, > > add new charge.) > > Accounting will be correct. > > > > Changelog (v2) -> (v3) > > - fixed invalid charge to swp_entry==0. > > - updated documentation. > > Changelog (v1) -> (v2) > > - fixed comment. > > > > Signed-off-by: KAMEZAWA Hiroyuki > > --- > > Documentation/controllers/memcg_test.txt | 41 +++++++++++++++++++++++++++---- > > mm/memcontrol.c | 7 +++-- > > mm/memory.c | 11 ++++---- > > 3 files changed, 46 insertions(+), 13 deletions(-) > > > > Index: mmotm-2.6.28-Dec12/mm/memory.c > > =================================================================== > > --- mmotm-2.6.28-Dec12.orig/mm/memory.c > > +++ mmotm-2.6.28-Dec12/mm/memory.c > > @@ -2428,22 +2428,23 @@ static int do_swap_page(struct mm_struct > > * while the page is counted on swap but not yet in mapcount i.e. > > * before page_add_anon_rmap() and swap_free(); try_to_free_swap() > > * must be called after the swap_free(), or it will never succeed. > > - * And mem_cgroup_commit_charge_swapin(), which uses the swp_entry > > - * in page->private, must be called before reuse_swap_page(), > > - * which may delete_from_swap_cache(). > > + * Because delete_from_swap_page() may be called by reuse_swap_page(), > > + * mem_cgroup_commit_charge_swapin() may not be able to find swp_entry > > + * in page->private. In this case, a record in swap_cgroup is silently > > + * discarded at swap_free(). > > */ > > > > - mem_cgroup_commit_charge_swapin(page, ptr); > > inc_mm_counter(mm, anon_rss); > > pte = mk_pte(page, vma->vm_page_prot); > > if (write_access && reuse_swap_page(page)) { > > pte = maybe_mkwrite(pte_mkdirty(pte), vma); > > write_access = 0; > > } > > - > > Removal of unassociated lines, not sure if that is a good practice. > my mistake... > > flush_icache_page(vma, page); > > set_pte_at(mm, address, page_table, pte); > > page_add_anon_rmap(page, vma, address); > > + /* It's better to call commit-charge after rmap is established */ > > + mem_cgroup_commit_charge_swapin(page, ptr); > > > > Yes, it does make sense > > > swap_free(entry); > > if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) > > Index: mmotm-2.6.28-Dec12/Documentation/controllers/memcg_test.txt > > =================================================================== > > --- mmotm-2.6.28-Dec12.orig/Documentation/controllers/memcg_test.txt > > +++ mmotm-2.6.28-Dec12/Documentation/controllers/memcg_test.txt > > @@ -1,6 +1,6 @@ > > Memory Resource Controller(Memcg) Implementation Memo. > > -Last Updated: 2008/12/10 > > -Base Kernel Version: based on 2.6.28-rc7-mm. > > +Last Updated: 2008/12/15 > > +Base Kernel Version: based on 2.6.28-rc8-mm. > > > > Because VM is getting complex (one of reasons is memcg...), memcg's behavior > > is complex. This is a document for memcg's internal behavior. > > @@ -111,9 +111,40 @@ Under below explanation, we assume CONFI > > (b) If the SwapCache has been mapped by processes, it has been > > charged already. > > > > - In case (a), we charge it. In case (b), we don't charge it. > > - (But racy state between (a) and (b) exists. We do check it.) > > - At charging, a charge recorded in swap_cgroup is moved to page_cgroup. > > + This swap-in is one of the most complicated work. In do_swap_page(), > > + following events occur when pte is unchanged. > > + > > + (1) the page (SwapCache) is looked up. > > + (2) lock_page() > > + (3) try_charge_swapin() > > + (4) reuse_swap_page() (may call delete_swap_cache()) > > + (5) commit_charge_swapin() > > + (6) swap_free(). > > + > > + Considering following situation for example. > > + > > + (A) The page has not been charged before (2) and reuse_swap_page() > > + doesn't call delete_from_swap_cache(). > > + (B) The page has not been charged before (2) and reuse_swap_page() > > + calls delete_from_swap_cache(). > > + (C) The page has been charged before (2) and reuse_swap_page() doesn't > > + call delete_from_swap_cache(). > > + (D) The page has been charged before (2) and reuse_swap_page() calls > > + delete_from_swap_cache(). > > + > > + memory.usage/memsw.usage changes to this page/swp_entry will be > > + Case (A) (B) (C) (D) > > + Event > > + Before (2) 0/ 1 0/ 1 1/ 1 1/ 1 > > + =========================================== > > + (3) +1/+1 +1/+1 +1/+1 +1/+1 > > + (4) - 0/ 0 - -1/ 0 > > + (5) 0/ 1 0/-1 -1/-1 0/ 0 > > + (6) - - - 0/-1 > > + =========================================== > > + Result 1/ 1 1/1 1/ 1 1/ 1 > > + > > + In any cases, charges to this page should be 1/ 1. > > > > The documentation patch failed to apply for me > Hmm... I'll check my queue again. Thanks, -Kame > > 4.2 Swap-out. > > At swap-out, typical state transition is below. > > Index: mmotm-2.6.28-Dec12/mm/memcontrol.c > > =================================================================== > > --- mmotm-2.6.28-Dec12.orig/mm/memcontrol.c > > +++ mmotm-2.6.28-Dec12/mm/memcontrol.c > > @@ -1139,10 +1139,11 @@ void mem_cgroup_commit_charge_swapin(str > > /* > > * Now swap is on-memory. This means this page may be > > * counted both as mem and swap....double count. > > - * Fix it by uncharging from memsw. This SwapCache is stable > > - * because we're still under lock_page(). > > + * Fix it by uncharging from memsw. Basically, this SwapCache is stable > > + * under lock_page(). But in do_swap_page()::memory.c, reuse_swap_page() > > + * may call delete_from_swap_cache() before reach here. > > */ > > - if (do_swap_account) { > > + if (do_swap_account && PageSwapCache(page)) { > > swp_entry_t ent = {.val = page_private(page)}; > > struct mem_cgroup *memcg; > > memcg = swap_cgroup_record(ent, NULL); > > > > > > > Looks good to me > > Acked-by: Balbir Singh > Tested-by: Balbir Singh > > -- > Balbir > -- 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/