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Re: [PATCH v4 1/6] xfs: reorganize xfs_iomap_prealloc_size to remove ind

To: Mark Tinguely <tinguely@xxxxxxx>
Subject: Re: [PATCH v4 1/6] xfs: reorganize xfs_iomap_prealloc_size to remove indentation
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Fri, 22 Feb 2013 13:08:56 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <5127A5E2.2070407@xxxxxxx>
References: <1361373019-30891-1-git-send-email-bfoster@xxxxxxxxxx> <1361373019-30891-2-git-send-email-bfoster@xxxxxxxxxx> <5127A5E2.2070407@xxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2
On 02/22/2013 12:07 PM, Mark Tinguely wrote:
> On 02/20/13 09:10, Brian Foster wrote:
>> The majority of xfs_iomap_prealloc_size() executes within the
>> check for lack of default I/O size. Reverse the logic to remove the
>> extra indentation.
>>
>> Signed-off-by: Brian Foster<bfoster@xxxxxxxxxx>
>> Reviewed-by: Dave Chinner<dchinner@xxxxxxxxxx>
>> Reviewed-by: Ben Myers<bpm@xxxxxxx>
>> ---
>>   fs/xfs/xfs_iomap.c |   63
>> ++++++++++++++++++++++++++-------------------------
>>   1 files changed, 32 insertions(+), 31 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
>> index 912d83d..d914419 100644
>> --- a/fs/xfs/xfs_iomap.c
>> +++ b/fs/xfs/xfs_iomap.c
>> @@ -381,42 +381,43 @@ xfs_iomap_prealloc_size(
>>       int            nimaps)
>>   {
>>       xfs_fsblock_t        alloc_blocks = 0;
>> +    int            shift = 0;
>> +    int64_t            freesp;
> 
> ...
> 
>> +    freesp = mp->m_sb.sb_fdblocks;
> 
> ...
> 
>> +    /*
>> +     * If we are still trying to allocate more space than is
>> +     * available, squash the prealloc hard. This can happen if we
>> +     * have a large file on a small filesystem and the above
>> +     * lowspace thresholds are smaller than MAXEXTLEN.
>> +     */
>> +    while (alloc_blocks>= freesp)
>> +        alloc_blocks>>= 4;
> 
> 
> Hi Brian, I am looking at your speculative preallocation quota
> throttling series.
> 
> I know this code is from commit 4d559a3b. would this not be bad of
> freesp == 0?
> 

Thanks. Hmm, I guess if freesp is 0 we'd hit an infinite loop
(irrespective of this patchset). We could change the comparison to >,
but I think the following would be more clear:

        while (alloc_blocks && alloc_blocks >= freesp)
                alloc_blocks >>= 4;

Thoughts? I'll send out a one-liner to bat around if that looks
reasonable. Good catch.

Brian

> --Mark.
> 

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