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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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