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SubjectRe: [RFC][BUGFIX][PATCH 1/2] memcg: fix charge bypass route of migration
On Thu, 15 Apr 2010 15:43:24 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Thu, 15 Apr 2010 12:05:16 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > I'd like to wait until next mmotm comes out. (So, [RFC]) I'll rebase
> > This patch is based on
> > mmotm-2010/04/05
> > +
> > mm-migration-take-a-reference-to-the-anon_vma-before-migrating.patch
> > mm-migration-do-not-try-to-migrate-unmapped-anonymous-pages.patch
> > mm-share-the-anon_vma-ref-counts-between-ksm-and-page-migration.patch
> > mm-migration-allow-the-migration-of-pageswapcache-pages.patch
> > memcg-fix-prepare-migration.patch
> >
> > ==
> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> >
> > This is an additonal fix to memcg-fix-prepare-migration.patch
> >
> > Now, try_charge can bypass charge if TIF_MEMDIE at el are marked on the caller.
> > In this case, the charge is bypassed. This makes accounts corrupted.
> > (PageCgroup will be marked as PCG_USED even if bypassed, and css->refcnt
> > can leak.)
> >
> > This patch clears passed "*memcg" in bypass route.
> >
> > Because usual page allocater passes memcg=NULL, this patch only affects
> > some special case as
> > - move account
> > - migration
> > - swapin.
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> > ---
> > mm/memcontrol.c | 7 +++++--
> > 1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > Index: mmotm-temp/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-temp.orig/mm/memcontrol.c
> > +++ mmotm-temp/mm/memcontrol.c
> > @@ -1606,8 +1606,12 @@ static int __mem_cgroup_try_charge(struc
> > * MEMDIE process.
> > */
> > if (unlikely(test_thread_flag(TIF_MEMDIE)
> > - || fatal_signal_pending(current)))
> > + || fatal_signal_pending(current))) {
> > + /* Showing we skipped charge */
> > + if (memcg)
> > + *memcg = NULL;
> > goto bypass;
> > + }
> >
> I'm sorry, I can't understand what this part fixes.
> We set *memcg to NULL at "bypass" part already:
>
> 1740 bypass:
> 1741 *memcg = NULL;
> 1742 return 0;
>
> and __mem_cgroup_try_charge() is never called with @memcg == NULL, IIUC.
>

I totally missed that..Sigh.


> > /*
> > * We always charge the cgroup the mm_struct belongs to.
> > @@ -2523,7 +2527,6 @@ int mem_cgroup_prepare_migration(struct
> > ret = __mem_cgroup_try_charge(NULL, GFP_KERNEL, ptr, false);
> > css_put(&mem->css);
> > }
> > - *ptr = mem;
> > return ret;
> > }
> >
> I sent a patch to Andrew to fix this part yesterday :)
>

Ok, ignore this patch.

-Kame



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