Messages in this thread Patch in this message | | | Date | Wed, 11 Jul 2012 18:57:43 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: [PATCH v2 -mm] memcg: prevent from OOM with too many dirty pages |
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Hi Michal,
On Wed, 20 Jun 2012, Michal Hocko wrote: > Hi Andrew, > here is an updated version if it is easier for you to drop the previous > one. > changes since v1 > * added Mel's Reviewed-by > * updated changelog as per Andrew > * updated the condition to be optimized for no-memcg case
I mentioned in Johannes's [03/11] thread a couple of days ago, that I was having a problem with your wait_on_page_writeback() in mmotm.
It turns out that your original patch was fine, but you let dark angels whisper into your ear, to persuade you to remove the "&& may_enter_fs".
Part of my load builds kernels on extN over loop over tmpfs: loop does mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS)) because it knows it will deadlock, if the loop thread enters reclaim, and reclaim tries to write back a dirty page, one which needs the loop thread to perform the write.
With the may_enter_fs check restored, all is well. I don't entirely like your patch: I think it would be much better to wait in the same place as the wait_iff_congested(), when the pages gathered have been sent for writing and unlocked and putback and freed; and I also wonder if it should go beyond the !global_reclaim case for swap pages, because they don't participate in dirty limiting.
But those are things I should investigate later - I did write a patch like that before, when I was having some unexpected OOM trouble with a private kernel; but my OOMs then were because of something silly that I'd left out, and I'm not at present sure if we have a problem in this regard or not.
The important thing is to get the may_enter_fs back into your patch: I can't really Sign-off the below because it's yours, but Acked-by: Hugh Dickins <hughd@google.com> ---
mm/vmscan.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- 3.5-rc6-mm1/mm/vmscan.c 2012-07-11 14:42:13.668335884 -0700 +++ linux/mm/vmscan.c 2012-07-11 16:01:20.712814127 -0700 @@ -726,7 +726,8 @@ static unsigned long shrink_page_list(st * writeback from reclaim and there is nothing else to * reclaim. */ - if (!global_reclaim(sc) && PageReclaim(page)) + if (!global_reclaim(sc) && PageReclaim(page) && + may_enter_fs) wait_on_page_writeback(page); else { nr_writeback++;
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