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    SubjectRe: [PATCH 4/4] blkcg: use radix tree to index blkgs from blkcg
    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 <>
    > Cc: Vivek Goyal <>

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

    Acked-by: Vivek Goyal <>


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