Messages in this thread |  | | | Date | Tue, 29 May 2012 11:08:57 +0800 | | From | Fengguang Wu <> | | Subject | Re: [RFC -mm] memcg: prevent from OOM with too many dirty pages |
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Hi Michal,
On Mon, May 28, 2012 at 05:38:55PM +0200, Michal Hocko wrote: > Current implementation of dirty pages throttling is not memcg aware which makes > it easy to have LRUs full of dirty pages which might lead to memcg OOM if the > hard limit is small and so the lists are scanned faster than pages written > back. > > This patch fixes the problem by throttling the allocating process (possibly > a writer) during the hard limit reclaim by waiting on PageReclaim pages. > We are waiting only for PageReclaim pages because those are the pages > that made one full round over LRU and that means that the writeback is much > slower than scanning. > The solution is far from being ideal - long term solution is memcg aware > dirty throttling - but it is meant to be a band aid until we have a real > fix.
IMHO it's still an important "band aid" -- perhaps worthwhile for sending to Greg's stable trees. Because it fixes a really important use case: it enables the users to put backups into a small memcg.
The users visible changes are:
the backup program get OOM killed => it runs now, although being a bit slow and bumpy
Talking about the more comprehensive fix, I'm sorry for delaying this patch for several months:
[PATCH 6/9] vmscan: dirty reclaim throttling http://thread.gmane.org/gmane.linux.kernel.mm/74582
Now that Jan's iput() avoidance patchset has just been merged by Linus, I'll rebase the patchset on top of his great work.
> diff --git a/mm/vmscan.c b/mm/vmscan.c > index c978ce4..7cccd81 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -720,9 +720,20 @@ static unsigned long shrink_page_list(struct list_head *page_list, > (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); > > if (PageWriteback(page)) { > - nr_writeback++; > - unlock_page(page); > - goto keep; > + /* > + * memcg doesn't have any dirty pages throttling so we > + * could easily OOM just because too many pages are in > + * writeback from reclaim and there is nothing else to > + * reclaim. > + */ > + if (PageReclaim(page) > + && may_enter_fs && !global_reclaim(sc)) > + wait_on_page_writeback(page); > + else { > + nr_writeback++; > + unlock_page(page); > + goto keep; > + } > } > > references = page_check_references(page, sc);
Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
This is all good for memcg. I'd suggest sending it to 3.5 and 3.4.x as well.
Thanks, Fengguang
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