linux-kernel - Re: [PATCH 7/12] ksm: fix endless loop on oom

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Date:	Tue, 04 Aug 2009 15:55:59 +0300
From:	Izik Eidus <ieidus@...hat.com>
To:	Hugh Dickins <hugh.dickins@...cali.co.uk>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Chris Wright <chrisw@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 7/12] ksm: fix endless loop on oom

Hugh Dickins wrote:
> break_ksm has been looping endlessly ignoring VM_FAULT_OOM: that should
> only be a problem for ksmd when a memory control group imposes limits
> (normally the OOM killer will kill others with an mm until it succeeds);
> but in general (especially for MADV_UNMERGEABLE and KSM_RUN_UNMERGE) we
> do need to route the error (or kill) back to the caller (or sighandling).
>
> Test signal_pending in unmerge_ksm_pages, which could be a lengthy
> procedure if it has to spill into swap: returning -ERESTARTSYS so that
> trivial signals will restart but fatals will terminate (is that right?
> we do different things in different places in mm, none exactly this).
>
> unmerge_and_remove_all_rmap_items was forgetting to lock when going
> down the mm_list: fix that.  Whether it's successful or not, reset
> ksm_scan cursor to head; but only if it's successful, reset seqnr
> (shown in full_scans) - page counts will have gone down to zero.
>
> This patch leaves a significant OOM deadlock, but it's a good step
> on the way, and that deadlock is fixed in a subsequent patch.
>
> Signed-off-by: Hugh Dickins <hugh.dickins@...cali.co.uk>
> ---
>
>
>   
Better than before for sure, And I dont have in mind better and yet 
simple solution for the "failing to break the pages" then to just wait 
and catch them in the next scan, so ACK.

Acked-by: Izik Eidus <ieidus@...hat.com>

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