Messages in this thread | | | Date | Fri, 17 Apr 2009 11:03:50 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [PATCH] Add file based RSS accounting for memory resource controller (v2) |
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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.
Thanks, -Kame
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