lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 12 Mar 2009 15:15:29 +0530 From: Balbir Singh <balbir@...ux.vnet.ibm.com> To: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org> Subject: Re: [BUGFIX][PATCH 1/5] memcg use correct scan number at reclaim * KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> [2009-03-12 16:45:59]: > > On Thu, 12 Mar 2009 09:44:14 +0530 > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote: > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-12 13:05:56]: > > > > > > > On Thu, 12 Mar 2009 09:30:54 +0530 > > > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote: > > > > > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-12 12:51:24]: > > > > > > > > > > > On Thu, 12 Mar 2009 09:19:18 +0530 > > > > > > Balbir Singh <balbir@...ux.vnet.ibm.com> wrote: > > > > > > > > > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-12 09:55:16]: > > > > > > > > > > > > > > > Andrew, this [1/5] is a bug fix, others are not. > > > > > > > > > > > > > > > > == > > > > > > > > From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> > > > > > > > > > > > > > > > > Even when page reclaim is under mem_cgroup, # of scan page is determined by > > > > > > > > status of global LRU. Fix that. > > > > > > > > > > > > > > > > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> > > > > > > > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> > > > > > > > > --- > > > > > > > > mm/vmscan.c | 2 +- > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > Index: mmotm-2.6.29-Mar10/mm/vmscan.c > > > > > > > > =================================================================== > > > > > > > > --- mmotm-2.6.29-Mar10.orig/mm/vmscan.c > > > > > > > > +++ mmotm-2.6.29-Mar10/mm/vmscan.c > > > > > > > > @@ -1470,7 +1470,7 @@ static void shrink_zone(int priority, st > > > > > > > > int file = is_file_lru(l); > > > > > > > > int scan; > > > > > > > > > > > > > > > > - scan = zone_page_state(zone, NR_LRU_BASE + l); > > > > > > > > + scan = zone_nr_pages(zone, sc, l); > > > > > > > > > > > > > > I have the exact same patch in my patch queue. BTW, mem_cgroup_zone_nr_pages is > > > > > > > buggy. We don't hold any sort of lock while extracting > > > > > > > MEM_CGROUP_ZSTAT (ideally we need zone->lru_lock). Without that how do > > > > > > > we guarantee that MEM_CGRUP_ZSTAT is not changing at the same time as > > > > > > > we are reading it? > > > > > > > > > > > > > Is it big problem ? We don't need very precise value and ZSTAT just have > > > > > > increment/decrement. So, I tend to ignore this small race. > > > > > > (and it's unsigned long, not long long.) > > > > > > > > > > > > > > > > The assumption is that unsigned long read is atomic even on 32 bit > > > > > systems? What if we get pre-empted in the middle of reading the data > > > > > and don't return back for long? The data can be highly in-accurate. > > > > > No? > > > > > > > > > Hmm, preempt_disable() is appropriate ? > > > > > > > > But shrink_zone() itself works on the value which is read at this time and > > > > dont' take care of changes in situation by preeemption...so it's not problem > > > > of memcg. > > > > > > > > > > You'll end up reclaiming based on old stale data. shrink_zone itself > > > maintains atomic data for zones. > > > > > IIUC, # of pages to be scanned is just determined once, here. > > In this case, lockless is right behavior. > lockless is valuable than precise ZSTAT. end user can't observe this race. > Lockless works fine provided the data is correctly aligned. I need to check this out more thoroghly. -- Balbir -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists