Re: [PATCH 4/4] blkcg: use radix tree to index blkgs from blkcg

[Vivek Goyal <vgoyal@xxxxxxxxxx>]

On Thu, Apr 19, 2012 at 04:29:24PM -0700, Tejun Heo wrote:
> blkg lookup is currently performed by traversing linked list anchored
> at blkcg->blkg_list.  This is very unscalable and with blk-throttle
> enabled and enough request queues on the system, this can get very
> ugly quickly (blk-throttle performs look up on every bio submission).
> 
> This patch makes blkcg use radix tree to index blkgs combined with
> simple last-looked-up hint.  This is mostly identical to how icqs are
> indexed from ioc.
> 
> Note that because __blkg_lookup() may be invoked without holding queue
> lock, hint is only updated from __blkg_lookup_create().  Due to cfq's
> cfqq caching, this makes hint updates overly lazy.  This will be
> improved with scheduled blkcg aware request allocation.
> 
> Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>

Nice to see radix tree lookup and caching hint. Helps with scalability.

Acked-by: Vivek Goyal <vgoyal@xxxxxxxxxx>

Vivek
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