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Re: [PATCH] mm, vmscan: Warn about possible deadlock at shirink_inactive

To: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH] mm, vmscan: Warn about possible deadlock at shirink_inactive_list
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 22 Sep 2015 07:52:41 +1000
Cc: xfs@xxxxxxxxxxx, linux-mm@xxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1442833794-23117-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx>
References: <1442833794-23117-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Sep 21, 2015 at 08:09:54PM +0900, Tetsuo Handa wrote:
> This is a difficult-to-trigger silent hang up bug.
> 
> The kswapd is allowed to bypass too_many_isolated() check in
> shrink_inactive_list(). But the kswapd can be blocked by locks in
> shrink_page_list() in shrink_inactive_list(). If the task which is
> blocking the kswapd is trying to allocate memory with the locks held,
> it forms memory reclaim deadlock.

It's a known problem in XFS and I'm currently working on patches to
fix it by hoisting the memory allocations outside of the CIL context
lock.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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