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[dm-devel] Re: [PATCH 19/23] io-controller: map async requests to appropriate cgroup

Vivek Goyal wrote:
o So far we were assuming that a bio/rq belongs to the task who is submitting
  it. It did not hold good in case of async writes. This patch makes use of
  blkio_cgroup pataches to attribute the aysnc writes to right group instead
  of task submitting the bio.

o For sync requests, we continue to assume that io belongs to the task
  submitting it. Only in case of async requests, we make use of io tracking
  patches to track the owner cgroup.

o So far cfq always caches the async queue pointer. With async requests now
  not necessarily being tied to submitting task io context, caching the
  pointer will not help for async queues. This patch introduces a new config
  option CONFIG_TRACK_ASYNC_CONTEXT. If this option is not set, cfq retains
  old behavior where async queue pointer is cached in task context. If it
  is set, async queue pointer is not cached and we take help of bio
  tracking patches to determine group bio belongs to and then map it to
  async queue of that group.

Signed-off-by: Nauman Rafique <nauman google com>
Signed-off-by: Gui Jianfeng <guijianfeng cn fujitsu com>
Signed-off-by: Vivek Goyal <vgoyal redhat com>

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

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