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    SubjectRe: [PATCH] Add file based RSS accounting for memory resource controller (v2)
    * 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?

    --
    Balbir


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