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Date: Fri, 30 Nov 2012 11:55:08 -0600
From: Mark Tinguely <tinguely@sgi.com>
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Subject: Re: [PATCH v2 1/3] xfs: use b_maps[] for discontiguous buffers
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	<20121128222622.688093599@sgi.com>
	<20121130160920.GA9873@infradead.org>
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To: Christoph Hellwig <hch@infradead.org>
Cc: xfs@oss.sgi.com

On 11/30/12 10:09, Christoph Hellwig wrote:
>>   use_alloc_page:
>> -	start = BBTOB(bp->b_map.bm_bn)>>  PAGE_SHIFT;
>> -	end = (BBTOB(bp->b_map.bm_bn + bp->b_length) + PAGE_SIZE - 1)
>> +	start = BBTOB(bp->b_maps[0].bm_bn)>>  PAGE_SHIFT;
>> +	end = (BBTOB(bp->b_maps[0].bm_bn + bp->b_length) + PAGE_SIZE - 1)
>
> Btw, how is this logic supposed to work for discontiguous buffers?
>
> Each of them might straddle boundaries individually, so doing the
> start/end calculation for the number of pages isn't going to be correct.
>

eeek. yep, I will loop through and count the pages needed in each
segment.

--Mark.

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