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blkcg: restructure blkg_policy_data allocation in blkcg_activate_policy()

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When a policy gets activated, it needs to allocate and install its
policy data on all existing blkg's (blkcg_gq's).  Because blkg
iteration is protected by a spinlock, it currently counts the total
number of blkg's in the system, allocates the matching number of
policy data on a list and installs them during a single iteration.

This can be simplified by using speculative GFP_NOWAIT allocations
while iterating and falling back to a preallocated policy data on
failure.  If the preallocated one has already been consumed, it
releases the lock, preallocate with GFP_KERNEL and then restarts the
iteration.  This can be a bit more expensive than before but policy
activation is a very cold path and shouldn't matter.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Tejun Heo
2015-08-18 14:55:09 -07:00
committed by Jens Axboe
parent bc915e61cd
commit 4c55f4f9ad
2 changed files with 21 additions and 37 deletions
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3
include/linux/blk-cgroup.h
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@@ -80,9 +80,6 @@ struct blkg_policy_data {
/* the blkg and policy id this per-policy data belongs to */
struct blkcg_gq *blkg;
int plid;
/* used during policy activation */
struct list_head alloc_node;
};
/*