linux-kernel - Re: [PATCH v2 01/14] block: Generalized bio pool freeing

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Message-ID: <20120524161914.GD27983@google.com>
Date:	Thu, 24 May 2012 09:19:14 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-bcache@...r.kernel.org,
	dm-devel@...hat.com, linux-fsdevel@...r.kernel.org,
	axboe@...nel.dk, agk@...hat.com, neilb@...e.de,
	drbd-dev@...ts.linbit.com, bharrosh@...asas.com, vgoyal@...hat.com,
	mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net
Subject: Re: [PATCH v2 01/14] block: Generalized bio pool freeing

On Thu, May 24, 2012 at 09:09:44AM -0700, Tejun Heo wrote:
> On Wed, May 23, 2012 at 05:02:38PM -0700, Kent Overstreet wrote:
> > With the old code, when you allocate a bio from a bio pool you have to
> > implement your own destructor that knows how to find the bio pool the
> > bio was originally allocated from.
> > 
> > This adds a new field to struct bio (bi_pool) and changes
> > bio_alloc_bioset() to use it. This makes various bio destructors
> > unnecessary, so they're then deleted.
> > 
> > Signed-off-by: Kent Overstreet <koverstreet@...gle.com>
> > Change-Id: I5eb66c1d6910757f4af8755b8857dcbe4619cf8d
> 
> Please drop Change-ID tag and it would be great how you tested the
> changes, other than that,
> 
>  Acked-by: Tejun Heo <tj@...nel.org>

To add a bit here too.  Please explain "why" you're making this
change.  Is it because bi_destructor interface is cumbersome?  Adding
bi_pool is overhead - why is it justified?  Is it because one pointer
is fine to add to struct bio (which I kinda agree) or are there future
changes which will reverse the overhead (which is the case here).

In general, I find the descriptions insufficient.  They don't describe
the reasons and reasoning behind the patch.

Thanks.

-- 
tejun
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