Messages in this thread | | | Date | Thu, 30 Apr 2009 23:42:46 +0530 | From | Balbir Singh <> | Subject | Re: [PATCH] memcg: fix stale swap cache leak v5 |
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* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-30 18:47:38]:
> On Thu, 30 Apr 2009 15:12:52 +0530 > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-30 18:04:26]: > > > > > On Thu, 30 Apr 2009 16:35:39 +0900 > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > > > > > On Thu, 30 Apr 2009 16:16:27 +0900 > > > > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > > > > > > > > > This is v5 but all codes are rewritten. > > > > > > > > > > After this patch, when memcg is used, > > > > > 1. page's swapcount is checked after I/O (without locks). If the page is > > > > > stale swap cache, freeing routine will be scheduled. > > > > > 2. vmscan.c calls try_to_free_swap() when __remove_mapping() fails. > > > > > > > > > > Works well for me. no extra resources and no races. > > > > > > > > > > Because my office will be closed until May/7, I'll not be able to make a > > > > > response. Posting this for showing what I think of now. > > > > > > > > > I found a hole immediately after posted this...sorry. plz ignore this patch/ > > > > see you again in the next month. > > > > > > > I'm now wondering to disable "swapin readahed" completely when memcg is used... > > > Then, half of the problems will go away immediately. > > > And it's not so bad to try to free swapcache if swap writeback ends. Then, another > > > half will go away... > > > > > > > Could you clarify? Will memcg not account for swapin readahead pages? > > > swapin-readahead pages are _not_ accounted now. (And I think _never_) > But has race and leak swp_entry account until global LRU runs. > > "Don't do swapin-readahead, at all" will remove following race completely. > == > CPU0 CPU1 > free_swap_and_cache() > read_swapcache_async() > == > swp_entry to be freed will not be read-in. > > I think there will no performance regression in _usual_ case even if no readahead. > But has no number yet. >
Kamezawa, Daisuke,
Can't we just correct the accounting and leave the page on the global LRU?
Daisuke in the race conditions mentioned is (2) significant? Since the accounting is already fixed during mem_cgroup_uncharge_page()?
-- Balbir
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