Messages in this thread | | | Date | Fri, 17 Apr 2009 12:17:26 +0530 | From | Balbir Singh <> | Subject | Re: [PATCH] Add file based RSS accounting for memory resource controller (v2) |
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* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-17 14:17:26]:
> On Fri, 17 Apr 2009 10:26:23 +0530 > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-17 12:49:51]: > > > > > On Fri, 17 Apr 2009 09:15:39 +0530 > > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-17 11:03:50]: > > > > > > > > > On Fri, 17 Apr 2009 07:10:42 +0530 > > > > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > > > > > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-17 09:14:59]: > > > > > > > > > > > > > On Thu, 16 Apr 2009 17:33:16 +0530 > > > > > > > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > > > > > > > > > > > > > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2009-04-16 17:15:35]: > > > > > > > > > > > > > > > > > > > > > > > > > > > Sorry, some troubles found. Ignore above Ack. 3points now. > > > > > > > > > > > > > > > > > > > > 1. get_cpu should be after (*) > > > > > > > > > > ==mem_cgroup_update_mapped_file_stat() > > > > > > > > > > + int cpu = get_cpu(); > > > > > > > > > > + > > > > > > > > > > + if (!page_is_file_cache(page)) > > > > > > > > > > + return; > > > > > > > > > > + > > > > > > > > > > + if (unlikely(!mm)) > > > > > > > > > > + mm = &init_mm; > > > > > > > > > > + > > > > > > > > > > + mem = try_get_mem_cgroup_from_mm(mm); > > > > > > > > > > + if (!mem) > > > > > > > > > > + return; > > > > > > > > > > + ----------------------------------------(*) > > > > > > > > > > + stat = &mem->stat; > > > > > > > > > > + cpustat = &stat->cpustat[cpu]; > > > > > > > > > > + > > > > > > > > > > + __mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_MAPPED_FILE, val); > > > > > > > > > > + put_cpu(); > > > > > > > > > > +} > > > > > > > > > > == > > > > > > > > > > > > > > > > Yes or I should have a goto > > > > > > > > > > > > > > > > > > > > > > > > > > > > 2. In above, "mem" shouldn't be got from "mm"....please get "mem" from page_cgroup. > > > > > > > > > > (Because it's file cache, pc->mem_cgroup is not NULL always.) > > > > > > > > > > > > > > > > Hmmm.. not sure I understand this part. Are you suggesting that mm can > > > > > > > > be NULL? > > > > > > > No. > > > > > > > > > > > > > > > I added the check for !mm as a safety check. Since this > > > > > > > > routine is only called from rmap context, mm is not NULL, hence mem > > > > > > > > should not be NULL. Did you find a race between mm->owner assignment > > > > > > > > and lookup via mm->owner? > > > > > > > > > > > > > > > No. > > > > > > > > > > > > > > page_cgroup->mem_cgroup != try_get_mem_cgroup_from_mm(mm); in many many cases. > > > > > > > > > > > > > > For example, libc and /bin/*** is tend to be loaded into default cgroup at boot but > > > > > > > used by many cgroups. But mapcount of page caches for /bin/*** is 0 if not running. > > > > > > > > > > > > > > Then, File_Mapped can be greater than Cached easily if you use mm->owner. > > > > > > > > > > > > > > I can't estimate RSS in *my* cgroup if File_Mapped includes pages which is under > > > > > > > other cgroups. It's meaningless. > > > > > > > Especially, when Cached==0 but File_Mapped > 0, I think "oh, the kernel leaks somehing..hmm..." > > > > > > > > > > > > > > By useing page_cgroup->mem_cgroup, we can avoid above mess. > > > > > > > > > > > > Yes, I see your point. I wanted mapped_file to show up in the cgroup > > > > > > that mapped the page. But this works for me as well, but that means > > > > > > we'll nest the page cgroup lock under the PTE lock. > > > > > > > > > > Don't worry. we do that nest at ANON's uncharge(), already. > > > > > > > > > > About cost: > > > > > > > > > > IIUC, the number of "mapcount 0->1/1->0" of file caches are much smaller than > > > > > that of o Anon. And there will be not very much cache pingpong. > > > > > > > > > > If you use PCG_MAPPED flag in page_cgroup (as my patch), you can use > > > > > not-atomic version of set/clear when update is only under lock_page_cgroup(). > > > > > If you find better way, plz use it. But we can't avoid some kind of atomic ops > > > > > for correct accounting, I think. > > > > > > > > > > > > > Can you sign off on your patch, so that I can take it with your > > > > signed-off-by. I will also make some minor changes, get_cpu() is not > > > > needed, since we are in preempt disable context. > > > > > > > Hmm, > > > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> > > > > > > But some more clean up is necesarry. > > > > > > === This part == > > > + lock_page_cgroup(pc); > > > + mem = pc->mem_cgroup; > > > + if (mem) { > > > + cpu = get_cpu(); > > > + stat = &mem->stat; > > > + cpustat = &stat->cpustat[cpu]; > > > + if (map) > > > > > > === Should be == > > > + lock_page_cgroup(pc); > > > if (!PageCgroupUsed(pc)) { > > > unlock_page_cgroup(pc); > > > return; > > > } > > > > Do we need this? If the page is mapped, pc should be used right? > > > > About file cache, it'd definitely charged at add-to-radix-tree > regardless of being mapped or not. >
Yes, what I meant was that before being mapped, the page should be charged by the memory controller.
> *But* we still have following code. > == > 820 static int __mem_cgroup_try_charge(struct mm_struct *mm, > 821 gfp_t gfp_mask, struct mem_cgroup **memcg, > 822 > 834 /* > 835 * We always charge the cgroup the mm_struct belongs to. > 836 * The mm_struct's mem_cgroup changes on task migration if the > 837 * thread group leader migrates. It's possible that mm is not > 838 * set, if so charge the init_mm (happens for pagecache usage). > 839 */ > 840 mem = *memcg; > 841 if (likely(!mem)) { > 842 mem = try_get_mem_cgroup_from_mm(mm); > 843 *memcg = mem; > 844 } else { > 845 css_get(&mem->css); > 846 } > 847 if (unlikely(!mem)) > 848 return 0; > == > > So, for _now_, we should use this style of checking page_cgroup is used or not. > Until we fix/confirm try_charge() does. >
Hmm... I think we need to fix this loop hole, if not mem, we should look at charging the root cgroup. I suspect !mem cases should be 0, I'll keep that as a TODO.
-- Balbir
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