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Re: [PATCH 00/30] xfsprogs: Initial CRC support

To: Jeff Liu <jeff.liu@xxxxxxxxxx>
Subject: Re: [PATCH 00/30] xfsprogs: Initial CRC support
From: "Michael L. Semon" <mlsemon35@xxxxxxxxx>
Date: Sat, 18 May 2013 02:27:19 -0400
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
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On 05/18/2013 01:07 AM, Jeff Liu wrote:

Looks our test for 32-bit system is insufficient.  There has another bug
reports regarding 32-bit yesterday:

I read this and did not chime in because I don't know about the "no space left on device" error.

The first issue the customer had, though, was one I had on a 2.8GHz Pentium 4. The idea of using a tunable to increase vmalloc space made me think, "What, am I using FreeBSD or something? Why didn't Linux auto-tune this?" so I dug deeper. [Disclaimer: I use FreeBSD and find value in it, but it requires at least some sysctl tuning for things that Linux will tune automatically.]

Basically, I had vmalloc space to have an environment set up perfectly in 768 MB of RAM. Then I added another 512 MB, and Linux saw only 896 MB for lack of highmem support. At that point I enabled highmem support, Linux decided to auto-tune my vmalloc space down to 128 MB, which was not enough to handle an xfsdump of a 30 GB device-mapper crypt partition. The PC, when left alone, could develop those same oops-y messages while doing incremental xfsdumps overnight, and if left alone for days, even simple cp commands could cause issues. My resolution was to use the CONFIG_VMSPLIT_2G kernel option and reduce the things reported by /proc/vmallocinfo that are vmalloc items. Some ioremap items in /proc/vmallocinfo were removed where convenient. Despite warnings on the Internet like "this breaks ELF" and "this breaks binary modules," I've had no issues with it in the nine months in which the kernel has operated this way. [Note: I don't use binary modules. For that matter, only that PC uses modules at all.] Ultimately, I got rid of the crypts as well, but not before verifying that the above setup did indeed solve the problem at hand.

It's only my two cents, one person trying to balance Internet research against what actually works in testing on one PC. If the solution is sane sane to you, feel free to forward this story to your customer to see if anything in it will help.

So I'm going to setup a 32-bit test environment for such tests together
with Michael.

Excellent! Let me know a little about your test environment and whether it's a VM or bare metal.


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