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Re: [Qemu-devel] [Qemu-block] [PATCH v5 0/2] block: enforce minimal 4096

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v5 0/2] block: enforce minimal 4096 alignment in qemu_blockalign
Date: Thu, 14 May 2015 11:13:03 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 13/05/2015 17:43, Stefan Hajnoczi wrote:
> A 64 MB buffer was given in the pwrite() call.
> The first and the last 128-page write requests may have partial
> pages, but why should the rest not use fully aligned 1024 sector
> writes?
> Maybe the buffer is split by the max sectors per request before
> the alignment requirements are considered.  It would be more
> efficient to first split off the unaligned parts.

Sounds like this could be it---then it's very similar to the issue
fixed by kernel commit c6e666345e1b (block: split discard into aligned
requests, 2012-08-02).


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