Re: iomap infrastructure and multipage writes V5

[xfs-owner@oss.sgi.com]

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From: Eric Sandeen <sandeen@sandeen.net>
To: Dave Chinner <david@fromorbit.com>, Christoph Hellwig <hch@lst.de>
Cc: rpeterso@redhat.com, linux-fsdevel@vger.kernel.org, xfs@oss.sgi.com
Subject: Re: iomap infrastructure and multipage writes V5
Date: Mon, 13 Feb 2017 16:31:55 -0600
Message-ID: <75a139c8-5e49-3a89-10d1-20caeef3f69a@sandeen.net>

On 8/2/16 6:42 PM, Dave Chinner wrote:
> On Sun, Jul 31, 2016 at 09:19:00PM +0200, Christoph Hellwig wrote:
>> Now after spending this much time I've started wondering why we even
>> reserve blocks in xfs_iomap_write_allocate - after all we've reserved
>> space for the actual data blocks and the indlen worst case in
>> xfs_bmapi_reserve_delalloc.  And in fact a little hack to drop that
>> reservation seems to solve both the root cause (depleted reserved pool)
>> and the cleanup mess.  I just haven't spend enought time to convince
>> myself that it's actually safe, and in fact looking at the allocator
>> makes me thing it only works by accident currently despite generally
>> postive test results.
>>
>> Here is the quick patch if anyone wants to chime in:
>>
>> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
>> index 620fc91..67c317f 100644
>> --- a/fs/xfs/xfs_iomap.c
>> +++ b/fs/xfs/xfs_iomap.c
>> @@ -717,7 +717,7 @@ xfs_iomap_write_allocate(
>>  
>>  		nimaps = 0;
>>  		while (nimaps == 0) {
>> -			nres = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
>> +			nres = 0; // XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
>>  
>>  			error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, nres,
>>  					0, XFS_TRANS_RESERVE, &tp);
>>
> 
> This solves the problem for me, and from history appears to be the
> right thing to do. Christoph, can you send a proper patch for this?

Did anything ever come of this?  I don't think I saw a patch, and it looks
like it is not upstream.

Thanks,
-Eric

> Cheers,
> 
> Dave.
>