linux-kernel - Re: 4.8.8 kernel trigger OOM killer repeatedly when I have lots of RAM that should be free

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Message-ID: <20161130203011.GB15989@htj.duckdns.org>
Date:   Wed, 30 Nov 2016 15:30:11 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Marc MERLIN <marc@...lins.org>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Jens Axboe <axboe@...com>, Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: 4.8.8 kernel trigger OOM killer repeatedly when I have lots of
 RAM that should be free

Hello,

On Wed, Nov 30, 2016 at 10:14:50AM -0800, Linus Torvalds wrote:
> Tejun/Kent - any way to just limit the workqueue depth for bcache?
> Because that really isn't helping, and things *will* time out and
> cause those problems when you have hundreds of IO's queued on a disk
> that likely as a write iops around ~100..

Yeah, easily.  I'm assuming it's gonna be the bcache_wq allocated in
from bcache_init().  It's currently using 0 as @max_active and it can
set to be any arbitrary number.  It'd be a very crude way to control
what looks like a buffer bloat with IOs tho.  We can make it a bit
more granular by splitting workqueues per bcache instance / purpose
but for the long term the right solution seems to be hooking into
writeback throttling mechanism that block layer just grew recently.

Thanks.

-- 
tejun