From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 1/5] block: Make generic_make_request handle arbitrary
 sized bios
Date: Mon, 25 Nov 2013 22:09:21 -0800
Message-ID: <20131126060921.GB6434@infradead.org>
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Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	axboe@kernel.dk, Neil Brown <neilb@suse.de>,
	Alasdair Kergon <agk@redhat.com>, dm-devel@redhat.com
To: Kent Overstreet <kmo@daterainc.com>
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> +	q->bio_split = bioset_create(4, 0);
> +	if (!q->bio_split)
> +		goto fail_id;

How did we arrive at a mempool size of 4 to make sure we can always make
progress with arbitrarily sized bios?  Shouldn't we document the design
decision somewhere?

> +static struct bio *blk_bio_discard_split(struct request_queue *q,
> +					 struct bio *bio,
> +					 struct bio_set *bs)
> +{

One fallout of this should be that it would allows us to impement
a range UNMAP/TRIP much more easily, which would help dramatically
with TRIM performance!