Messages in this thread | | | Date | Wed, 5 Jan 2011 13:48:50 +0900 | Subject | Re: [BUGFIX][PATCH] memcg: fix memory migration of shmem swapcache | From | Minchan Kim <> |
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Hi,
On Wed, Jan 5, 2011 at 1:00 PM, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > Hi. > > This is a fix for a problem which has bothered me for a month. > > === > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > In current implimentation, mem_cgroup_end_migration() decides whether the page > migration has succeeded or not by checking "oldpage->mapping". > > But if we are tring to migrate a shmem swapcache, the page->mapping of it is > NULL from the begining, so the check would be invalid. > As a result, mem_cgroup_end_migration() assumes the migration has succeeded > even if it's not, so "newpage" would be freed while it's not uncharged. > > This patch fixes it by passing mem_cgroup_end_migration() the result of the > page migration. > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Nice catch. I don't oppose the patch. But as looking the code in unmap_and_move, I feel part of mem cgroup migrate is rather awkward.
int unmap_and_move() { charge = mem_cgroup_prepare_migration(xxx); .. BUG_ON(charge); <-- BUG if it is charged? .. uncharge: if (!charge) <-- why do we have to uncharge !charge? mem_group_end_migration(xxx); .. }
'charge' local variable isn't good. How about changing "uncharge" or whatever? Of course, It would be another patch. If you don't mind, I will send the patch or you may send the patch.
Thanks,
-- Kind regards, Minchan Kim
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