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SubjectRe: [PATCH -mmotm 3/4] memcg: dirty pages accounting and limiting infrastructure
* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-03-05 10:58:55]:

> On Fri, 5 Mar 2010 10:12:34 +0900
> Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
>
> > On Thu, 4 Mar 2010 11:40:14 +0100, Andrea Righi <arighi@develer.com> wrote:
> > > Infrastructure to account dirty pages per cgroup and add dirty limit
> > > static int mem_cgroup_count_children_cb(struct mem_cgroup *mem, void *data)
> > > {
> > > int *val = data;
> > > @@ -1275,34 +1423,70 @@ static void record_last_oom(struct mem_cgroup *mem)
> > > }
> > >
> > > /*
> > > - * Currently used to update mapped file statistics, but the routine can be
> > > - * generalized to update other statistics as well.
> > > + * Generalized routine to update file cache's status for memcg.
> > > + *
> > > + * Before calling this, mapping->tree_lock should be held and preemption is
> > > + * disabled. Then, it's guarnteed that the page is not uncharged while we
> > > + * access page_cgroup. We can make use of that.
> > > */
> > IIUC, mapping->tree_lock is held with irq disabled, so I think "mapping->tree_lock
> > should be held with irq disabled" would be enouth.
> > And, as far as I can see, callers of this function have not ensured this yet in [4/4].
> >
> > how about:
> >
> > void mem_cgroup_update_stat_locked(...)
> > {
> > ...
> > }
> >
> > void mem_cgroup_update_stat_unlocked(mapping, ...)
> > {
> > spin_lock_irqsave(mapping->tree_lock, ...);
> > mem_cgroup_update_stat_locked();
> > spin_unlock_irqrestore(...);
> > }
> >
> Rather than tree_lock, lock_page_cgroup() can be used if tree_lock is not held.
>
> lock_page_cgroup();
> mem_cgroup_update_stat_locked();
> unlock_page_cgroup();
>
> Andrea-san, FILE_MAPPED is updated without treelock, at least. You can't depend
> on migration_lock about FILE_MAPPED.
>

FILE_MAPPED is updated under pte lock in the rmap context and
page_cgroup lock within update_file_mapped.


--
Three Cheers,
Balbir


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