linux-kernel - Re: endless sync on bdi_sched

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Message-ID: <x49634b9bgh.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 01 Apr 2010 16:14:54 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	Denys Fedorysychenko <nuclearcat@...learcat.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: endless sync on bdi_sched_wait()? 2.6.33.1

Dave Chinner <david@...morbit.com> writes:

> On Thu, Apr 01, 2010 at 01:42:42PM +0300, Denys Fedorysychenko wrote:
>> Thats correct, it is quite busy cache server.
>> 
>> Well, if i stop squid(cache) sync will finish enough fast.
>> If i don't - it took more than hour. Actually i left that PC after 1 hour, and 
>> it didn't finish yet. I don't think it is normal.
>> Probably sync taking new data and trying to flush it too, and till he finish 
>> that, more data comes. 
>> Actually all what i need - to sync config directory. I cannot use fsync, 
>> because it is multiple files opened before by other processes, and sync is 
>> doing trick like this. I got dead process, and only fast way to recover system 
>> - kill the cache process, so I/O pumping will stop for a while, and sync() 
>> will have chance to finish.
>> Sure there is way just to "remount" config partition to ro, but i guess just 
>> sync must flush only current buffer cache pages.
>> 
>> I will do more tests now and will give exact numbers, how much time it needs 
>> with running squid and if i kill it shortly after running sync.
>
> Ok. What would be interesting is regular output from /proc/meminfo
> to see how the dirty memory is changing over the time the sync is
> running....

This sounds familiar:

http://lkml.org/lkml/2010/2/12/41

Cheers,
Jeff
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