Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754609AbYLOIhm (ORCPT ); Mon, 15 Dec 2008 03:37:42 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752125AbYLOIhe (ORCPT ); Mon, 15 Dec 2008 03:37:34 -0500 Received: from e28smtp03.in.ibm.com ([59.145.155.3]:57894 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752018AbYLOIhd (ORCPT ); Mon, 15 Dec 2008 03:37:33 -0500 Date: Mon, 15 Dec 2008 14:07:26 +0530 From: Balbir Singh To: KAMEZAWA Hiroyuki 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: <20081215083726.GH18403@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com Mail-Followup-To: KAMEZAWA Hiroyuki , Hugh Dickins , Daisuke Nishimura , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20081215160751.b6a944be.kamezawa.hiroyu@jp.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7169 Lines: 179 * 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. > 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 > 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/