linux-kernel - Re: [PATCH V3] bio: modify __bio_add_page() to accept pages that don't start a new segment

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Message-ID: <20140527115859.GA30458@dhcp-27-189.brq.redhat.com>
Date:	Tue, 27 May 2014 13:58:59 +0200
From:	Maurizio Lombardi <mlombard@...hat.com>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"James E.J. Bottomley" <JBottomley@...allels.com>,
	Christoph Hellwig <hch@....de>, linux-scsi@...r.kernel.org,
	Kent Overstreet <kmo@...erainc.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	m.lombardi85@...il.com
Subject: Re: [PATCH V3] bio: modify __bio_add_page() to accept pages that
 don't start a new segment

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
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