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Re: [PATCH 4/4] xfs: obey minleft values during extent allocation correc

To: Lachlan McIlroy <lmcilroy@xxxxxxxxxx>
Subject: Re: [PATCH 4/4] xfs: obey minleft values during extent allocation correctly.
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 21 Apr 2011 16:53:12 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1990267029.169210.1303362318856.JavaMail.root@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
References: <1303360144-10632-5-git-send-email-david@xxxxxxxxxxxxx> <1990267029.169210.1303362318856.JavaMail.root@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
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On Thu, Apr 21, 2011 at 01:05:18AM -0400, Lachlan McIlroy wrote:
> ----- Original Message -----
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> > 
> > When allocating an extent that is long enough to consume the
> > remaining free space in an AG, we need to ensure that the allocation
> > leaves enough space in the AG for any subsequent bmap btree blocks
> > that are needed to track the new extent. These have to be allocated
> > in the same AG as we only reserve enough blocks in an allocation
> > transaction for modification of the freespace trees in a single AG.
> > 
> > xfs_alloc_fix_minleft() has been considering blocks on the AGFL as
> > free blocks available for extent and bmbt block allocation, which is
> > not correct - blocks on the AGFL are there exclusively for the use
> > of the free space btrees. As a result, when minleft is less than the
> > number of blocks on the AGFL, xfs_alloc_fix_minleft() does not trim
> > the given extent to leave minleft blocks available for bmbt
> > allocation, and hence we can fail allocation during bmbt record
> > insertion.
> > 
> > A further problem is that bmbt block allocation doesn't set the
> > total number of blocks correctly for the allocation, thereby
> > allowing it to allocate a block from the AGFL before failing on the
> > second block in xfs_alloc_fix_freelist(). The total needs to be set
> > so that it skips AGs that only have the minimum reserved
> > amount of AGFL blocks free in them.
> > 
> > Similarly, xfs_inobt_alloc_block() needs to set args->total as well.
> Dave, you seem to have dropped the args->total changes?

yeah I did - I forgot to update the commit message. It passes test
250 without the args.total changes, so I figured that the minimum
change needed was the best approach. I'll fix the commit message.


Dave Chinner

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