linux-kernel - Re: swap_cluster

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Date:   Fri, 17 Feb 2017 10:07:15 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        "Huang\, Ying" <ying.huang@...el.com>,
        Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: swap_cluster_info lockdep splat

Hi, Hugh,

Hugh Dickins <hughd@...gle.com> writes:

> On Thu, 16 Feb 2017, Tim Chen wrote:
>> 
>> > I do not understand your zest for putting wrappers around every little
>> > thing, making it all harder to follow than it need be.  Here's the patch
>> > I've been running with (but you have a leak somewhere, and I don't have
>> > time to search out and fix it: please try sustained swapping and swapoff).
>> > 
>> 
>> Hugh, trying to duplicate your test case.  So you were doing swapping,
>> then swap off, swap on the swap device and restart swapping?
>
> Repeated pair of make -j20 kernel builds in 700M RAM, 1.5G swap on SSD,
> 8 cpus; one of the builds in tmpfs, other in ext4 on loop on tmpfs file;
> sizes tuned for plenty of swapping but no OOMing (it's an ancient 2.6.24
> kernel I build, modern one needing a lot more space with a lot less in use).
>
> How much of that is relevant I don't know: hopefully none of it, it's
> hard to get the tunings right from scratch.  To answer your specific
> question: yes, I'm not doing concurrent swapoffs in this test showing
> the leak, just waiting for each of the pair of builds to complete,
> then tearing down the trees, doing swapoff followed by swapon, and
> starting a new pair of builds.
>
> Sometimes it's the swapoff that fails with ENOMEM, more often it's a
> fork during build that fails with ENOMEM: after 6 or 7 hours of load
> (but timings show it getting slower leading up to that).  /proc/meminfo
> did not give me an immediate clue, Slab didn't look surprising but
> I may not have studied close enough.

Thanks for you information!

Memory newly allocated in the mm-swap series are allocated via vmalloc,
could you find anything special for vmalloc in /proc/meminfo?

Best Regards,
Huang, Ying

> I quilt-bisected it as far as the mm-swap series, good before, bad
> after, but didn't manage to narrow it down further because of hitting
> a presumably different issue inside the series, where swapoff ENOMEMed
> much sooner (after 25 mins one time, during first iteration the next).
>
> Hugh