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Date: Tue, 27 May 2014 13:58:59 +0200
From: Maurizio Lombardi <mlombard@redhat.com>
To: Ming Lei <tom.leiming@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
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        Kent Overstreet <kmo@daterainc.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        m.lombardi85@gmail.com
Subject: Re: [PATCH V3] bio: modify __bio_add_page() to accept pages that
 don't start a new segment
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On Tue, May 27, 2014 at 06:15:45PM +0800, Ming Lei wrote:
> 
> If the page can be merged to last segment, it should have been
> covered by code in branch of 'if (bio->bi_vcnt > 0) ...', shouldn't it?
> 
> Or maybe it is better to make that code cover your case since
> looks your case is similar with that one according to your commit
> log.
>

I realized that maybe you mean this branch:

if (bio->bi_vcnt > 1 && (BIOVEC_PHYS_MERGEABLE(bvec-1, bvec)))

right?
In this case the branch is not even reached in the original code because
the function returned an error way before executing it (line 760)

There was already a patchset trying to modify the code in a different way than mine:

https://groups.google.com/forum/#!msg/linux.kernel/3IanUpBVhFQ/3Xbg3yLRFp4J

but it has been ignored and in my opinion it takes a more
complicated approach.

Regards,
Maurizio Lombardi