From: Vasily Tarasov <vtaras@openvz.org>
Date: Wed, 25 Apr 2007 10:29:51 +0000 (+0200)
Subject: cfq-iosched: get rid of cfqq hash
X-Git-Tag: v2.6.22-rc1~1108^2^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=91fac317a34859986a2359a5a5c0e37dc17a9c3d;p=pandora-kernel.git

cfq-iosched: get rid of cfqq hash

cfq hash is no more necessary.  We always can get cfqq from io context.
cfq_get_io_context_noalloc() function is introduced, because we don't
want to allocate cic on merging and checking may_queue.  In order to
identify sync queue we've used hash key = CFQ_KEY_ASYNC. Since hash is
eliminated we need to use other criterion: sync flag for queue is added.
In all places where we dig in rb_tree we're in current context, so no
additional locking is required.

Advantages of this patch: no additional memory for hash, no seeking in
hash, code is cleaner. But it is necessary now to seek cic in per-ioc
rbtree, but it is faster:
- most processes work only with few devices
- most systems have only few block devices
- it is a rb-tree

Signed-off-by: Vasily Tarasov <vtaras@openvz.org>

Changes by me:

- Merge into CFQ devel branch
- Get rid of cfq_get_io_context_noalloc()
- Fix various bugs with dereferencing cic->cfqq[] with offset other
  than 0 or 1.
- Fix bug in cfqq setup, is_sync condition was reversed.
- Fix bug where only bio_sync() is used, we need to check for a READ too

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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