linux-kernel - Re: Page Allocation Failures/OOM with dm-crypt on software RAID10 (Intel Rapid Storage)

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Date:	Tue, 12 Jul 2016 16:56:32 +0200
From:	Matthias Dahl <ml_linux-kernel@...ary-island.eu>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	linux-raid@...r.kernel.org, linux-mm@...ck.org,
	dm-devel@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: Page Allocation Failures/OOM with dm-crypt on software RAID10
 (Intel Rapid Storage)

Hello Michal...

On 2016-07-12 16:07, Michal Hocko wrote:

> /proc/slabinfo could at least point on who is eating that memory.

Thanks. I have made another test (and thus again put the RAID10 out of
sync for the 100th time, sigh) and made regular snapshots of slabinfo
which I have attached to this mail.

> Direct IO doesn't get throttled like buffered IO.

Is buffered i/o not used in both cases if I don't explicitly request
direct i/o?

     dd if=/dev/zero /dev/md126p5 bs=512K
and dd if=/dev/zero /dev/mapper/test-device bs=512K

Given that the test-device is dm-crypt on md125p5. Aren't both using
buffered i/o?

> the number of pages under writeback was more or less same throughout
> the time but there are some local fluctuations when some pages do get
> completed.

The pages under writeback are those directly destined for the disk, so
after dm-crypt had done its encryption?

> If not you can enable allocator trace point for a particular object
> size (or range of sizes) and see who is requesting them.

If that support is baked into the Fedora provided kernel that is. If
you could give me a few hints or pointers, how to properly do a 
allocator
trace point and get some decent data out of it, that would be nice.

Thanks,
Matthias

-- 
Dipl.-Inf. (FH) Matthias Dahl | Software Engineer | binary-island.eu
  services: custom software [desktop, mobile, web], server administration
Download attachment "slabinfo.txt.gz" of type "application/x-gzip" (30968 bytes)