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    SubjectRe: [PATCH 20/23] io-controller: Per cgroup request descriptor support
    Vivek Goyal wrote:
    > o Currently a request queue has got fixed number of request descriptors for
    > sync and async requests. Once the request descriptors are consumed, new
    > processes are put to sleep and they effectively become serialized. Because
    > sync and async queues are separate, async requests don't impact sync ones
    > but if one is looking for fairness between async requests, that is not
    > achievable if request queue descriptors become bottleneck.
    >
    > o Make request descriptor's per io group so that if there is lots of IO
    > going on in one cgroup, it does not impact the IO of other group.
    >
    > o This patch implements the per cgroup request descriptors. request pool per
    > queue is still common but every group will have its own wait list and its
    > own count of request descriptors allocated to that group for sync and async
    > queues. So effectively request_list becomes per io group property and not a
    > global request queue feature.
    >
    > o Currently one can define q->nr_requests to limit request descriptors
    > allocated for the queue. Now there is another tunable q->nr_group_requests
    > which controls the requests descriptr limit per group. q->nr_requests
    > supercedes q->nr_group_requests to make sure if there are lots of groups
    > present, we don't end up allocating too many request descriptors on the
    > queue.
    >
    > Signed-off-by: Nauman Rafique <nauman@google.com>
    > Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

    Acked-by: Rik van Riel <riel@redhat.com>


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