Messages in this thread |  | | | Date | Thu, 30 Apr 2009 09:03:13 +0900 | | From | KAMEZAWA Hiroyuki <> | | Subject | Re: [PATCH] fix leak of swap accounting as stale swap cache under memcg |
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On Wed, 29 Apr 2009 03:16:06 +0530 Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-28 08:57:53]: > > > On Tue, 28 Apr 2009 00:47:31 +0530 > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > > > Thanks for the detailed explanation of the possible race conditions. I > > > am beginning to wonder why we don't have any hooks in add_to_swap.*. > > > for charging a page. If the page is already charged and if it is a > > > context issue (charging it to the right cgroup) that is already > > > handled from what I see. Won't that help us solve the !PageCgroupUsed > > > issue? > > > > > > > For adding hook to add_to_swap_cache, we need to know which cgroup the swap cache > > should be charged. Then, we have to remove CONFIG_CGROUP_MEM_RES_CTRL_SWAP_EXT > > and enable memsw control always. > > > > When using swap_cgroup, we'll know which cgroup the new swap cache should be charged. > > Then, the new page readed in will be charged to recorded cgroup in swap_cgroup. > > One bad thing of this method is a cgroup which swap_cgroup point to is different from > > a cgroup which the task calls do_swap_fault(). This means that a page-fault by a > > task can cause memory-reclaim under another cgroup and moreover, OOM. > > I don't think it's sane behavior. So, current design of swap accounting waits until the > > page is mapped. > > > > I know (that is why we removed the hooks from the original memcg at > some point). Why can't we mark the page here as swap pending to be > mapped, so that we don't lose them. As far as OOM is concerned, I > think they'll get relocated again when they are mapped (as per the > current implementation), the ones that don't are stale and can be > easily reclaimed.
My point is "we need a help of global LRU". To implement softlimit, we *have to* fix this without global LRU's help. I have much more simple patch. pls see it.
Thanks, -Kame
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