From: Mikulas Patocka <mpatocka@redhat.com>
Date: Fri, 12 Oct 2012 20:02:15 +0000 (+0100)
Subject: dm: store dm_target_io in bio front_pad
X-Git-Tag: v3.7-rc1~21^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dba141601d1327146c84b575bd581ea8730e901c;p=pandora-kernel.git

dm: store dm_target_io in bio front_pad

Use the recently-added bio front_pad field to allocate struct dm_target_io.

Prior to this patch, dm_target_io was allocated from a mempool. For each
dm_target_io, there is exactly one bio allocated from a bioset.

This patch merges these two allocations into one allocation: we create a
bioset with front_pad equal to the size of dm_target_io so that every
bio allocated from the bioset has sizeof(struct dm_target_io) bytes
before it. We allocate a bio and use the bytes before the bio as
dm_target_io.

_tio_cache is removed and the tio_pool mempool is now only used for
request-based devices.

This idea was introduced by Kent Overstreet.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Kent Overstreet <koverstreet@google.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: tj@kernel.org
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Bill Pemberton <wfp5p@viridian.itc.virginia.edu>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
---

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