Message-ID: <4AB08744.1020102@primeinteractive.net>
Date: Wed, 16 Sep 2009 08:35:48 +0200
From: Pavol Cvengros <pavol.cvengros@primeinteractive.net>
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To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
CC: Jan Kara <jack@suse.cz>, Justin Maggard <jmaggard10@gmail.com>,
       Eric Sandeen <sandeen@redhat.com>, Jiri Kosina <jkosina@suse.cz>,
       linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org
Subject: Re: ext4+quota+nfs issue
References: <4AA5E5F3.30309@primeinteractive.net> <4AA72C14.1020005@primeinteractive.net> <alpine.LRH.2.00.0909091141300.25928@twin.jikos.cz> <4AA7C38E.8020306@redhat.com> <150c16850909091045h1962fd67n77c265c9b99c5f44@mail.gmail.com> <4AA7FBD7.9080406@primeinteractive.net> <4AAA5FCC.2010707@primeinteractive.net> <20090914175056.GE25549@duck.suse.cz> <20090914185228.GA5984@skywalker.linux.vnet.ibm.com>
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On 9/14/2009 8:52 PM, Aneesh Kumar K.V wrote:
> On Mon, Sep 14, 2009 at 07:50:56PM +0200, Jan Kara wrote:
>    
>>    I've found some time to look into this and I can see a few problems in
>> the code. Firstly, what may cause your problems:
>>    vfs_dq_claim_blocks() is called in ext4_mb_mark_diskspace_used(). But
>> as far as I can understand the code, ext4_mb_normalize_request() can
>> increase the amount of space we really allocate and thus we try to
>> allocate more blocks than we have actually reserved in quota. Aneesh, is
>> that right?
>>      
> ext4_mb_mark_diskspace_used use ac->ac_b_ex.fe_len which is NOT the normalized
> request len. it is min(allocated_len, original_len). So i guess that code
> should be safe
>
>
>    
>>    Secondly, ext4_da_reserve_space() seems to have a bug that it can reserve
>> quota blocks multiple times if ext4_claim_free_blocks() fail and we retry
>> the allocation. We should release the quota reservation before restarting.
>> Actually, when we find out we cannot reserve quota space, we could force
>> some delayed allocated writes to disk (thus possibly release some quota
>> in case we have overestimated the amount of blocks needed). But that's
>> a different issue.
>>      
> That would imply the file system was full. But the dumpe2fs ouput list
> large number of free blocks. But yes the code should have released the
> quota reservation before trying block reservation again.
>
>
>    

file system is fresh but unfortunately already used and I can't 
"re-format" it. Is there a way around this? I think that FS was created 
by "mkfs.ext4 -j /dev....."

>>    Thirdly, ext4_indirect_calc_metadata_amount() is wrong for sparse files.
>> The worst case is 3 metadata blocks per data block if we make the file
>> sufficiently sparse and there's no easy way around that...
>>
>>      
> -aneesh
>    

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