Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

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On Thu, Feb 24, 2011 at 10:19 AM, Chris Mason <chris.mason@xxxxxxxxxx> wrote:
> Excerpts from Mitch Harder's message of 2011-02-24 11:03:07 -0500:
>> On Thu, Feb 24, 2011 at 10:00 AM, Chris Mason <chris.mason@xxxxxxxxxx> wrote:
>> > Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -0500:
>> >> 2011/2/24 Maria Wikström <maria@xxxxxxxxxxxxx>:
>> >> > mån 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
>> >> >> The backtrace in your attachment looks like a known bug of 2.6.37 which have already been fixed in 2.6.38. I have no idea why latest btrfs still hang in your environment if there's no debug info...
>> >> >>
>> >> >
>> >> > Haha, yes that's very hard :)
>> >> >
>> >> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can close the
>> >> > process with ctrl+c and it disappear a few seconds later. There is no
>> >> > CPU usage. Reading works because I can start htop and watch "svn info"
>> >> > disappear, but everything writing to btrfs slows down to a crawl. It
>> >> > takes about 1 minute to log in. So I had to put the logs on an other
>> >> > partition using ext3 to get the output from sysrq+t.
>> >> >
>> >>
>> >> I believe I've been experiencing this issue also.  However, my problem
>> >> usually results in a "No space left on device" error rather than a
>> >> lock-up or crash.  But I've bisected my issue to this patch, and my
>> >> "btrfs fi show" and "btrfs fi df" looks similar to others who've
>> >> posted to this tread with all my space being allocated, but not used.
>> >>
>> >
>> > Sorry, which patch did you bisect the problem down to?
>> >
>>
>> The patch at the head of this thread:
>>
>> Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
>
> Hmmm, that patch shouldn't be changing our performance under delalloc
> pressure, and it really shouldn't impact early enospc.
>

I've bisected this issue around where this patch went into git, and
I've also constructed a testing patch that reverts this patch, and
placed it on top of the current Btrfs git sources (I understand this
patch addresses a real issue, this was just for testing).

It could be that this patch just "uncovers" another problem, but all
my tests seem to point to this patch triggering this issue.
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