On Tue 18-06-24 11:27:53, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> After commit 35fe6d763229 ("block: use standard blktrace API to output
> cgroup info for debug notes"), the field 'bfqg->blkg_path' is not used
> and hence can be removed, and therefor blkg_path() is not used anymore
> and can be removed.
>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
Yay, nice to see code removed! Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> block/bfq-cgroup.c | 51 ---------------------------------------------
> block/bfq-iosched.h | 3 ---
> block/blk-cgroup.h | 13 ------------
> 3 files changed, 67 deletions(-)
>
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index d442ee358fc2..b758693697c0 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -797,57 +797,6 @@ void bfq_bic_update_cgroup(struct bfq_io_cq *bic, struct bio *bio)
> */
> bfq_link_bfqg(bfqd, bfqg);
> __bfq_bic_change_cgroup(bfqd, bic, bfqg);
> - /*
> - * Update blkg_path for bfq_log_* functions. We cache this
> - * path, and update it here, for the following
> - * reasons. Operations on blkg objects in blk-cgroup are
> - * protected with the request_queue lock, and not with the
> - * lock that protects the instances of this scheduler
> - * (bfqd->lock). This exposes BFQ to the following sort of
> - * race.
> - *
> - * The blkg_lookup performed in bfq_get_queue, protected
> - * through rcu, may happen to return the address of a copy of
> - * the original blkg. If this is the case, then the
> - * bfqg_and_blkg_get performed in bfq_get_queue, to pin down
> - * the blkg, is useless: it does not prevent blk-cgroup code
> - * from destroying both the original blkg and all objects
> - * directly or indirectly referred by the copy of the
> - * blkg.
> - *
> - * On the bright side, destroy operations on a blkg invoke, as
> - * a first step, hooks of the scheduler associated with the
> - * blkg. And these hooks are executed with bfqd->lock held for
> - * BFQ. As a consequence, for any blkg associated with the
> - * request queue this instance of the scheduler is attached
> - * to, we are guaranteed that such a blkg is not destroyed, and
> - * that all the pointers it contains are consistent, while we
> - * are holding bfqd->lock. A blkg_lookup performed with
> - * bfqd->lock held then returns a fully consistent blkg, which
> - * remains consistent until this lock is held.
> - *
> - * Thanks to the last fact, and to the fact that: (1) bfqg has
> - * been obtained through a blkg_lookup in the above
> - * assignment, and (2) bfqd->lock is being held, here we can
> - * safely use the policy data for the involved blkg (i.e., the
> - * field bfqg->pd) to get to the blkg associated with bfqg,
> - * and then we can safely use any field of blkg. After we
> - * release bfqd->lock, even just getting blkg through this
> - * bfqg may cause dangling references to be traversed, as
> - * bfqg->pd may not exist any more.
> - *
> - * In view of the above facts, here we cache, in the bfqg, any
> - * blkg data we may need for this bic, and for its associated
> - * bfq_queue. As of now, we need to cache only the path of the
> - * blkg, which is used in the bfq_log_* functions.
> - *
> - * Finally, note that bfqg itself needs to be protected from
> - * destruction on the blkg_free of the original blkg (which
> - * invokes bfq_pd_free). We use an additional private
> - * refcounter for bfqg, to let it disappear only after no
> - * bfq_queue refers to it any longer.
> - */
> - blkg_path(bfqg_to_blkg(bfqg), bfqg->blkg_path, sizeof(bfqg->blkg_path));
> bic->blkcg_serial_nr = serial_nr;
> }
>
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 467e8cfc41a2..08ddf2cfae5b 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -1003,9 +1003,6 @@ struct bfq_group {
> /* must be the first member */
> struct blkg_policy_data pd;
>
> - /* cached path for this blkg (see comments in bfq_bic_update_cgroup) */
> - char blkg_path[128];
> -
> /* reference counter (see comments in bfq_bic_update_cgroup) */
> refcount_t ref;
>
> diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
> index 25833221a12b..6dcaf63c560a 100644
> --- a/block/blk-cgroup.h
> +++ b/block/blk-cgroup.h
> @@ -301,19 +301,6 @@ static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
> return cpd ? cpd->blkcg : NULL;
> }
>
> -/**
> - * blkg_path - format cgroup path of blkg
> - * @blkg: blkg of interest
> - * @buf: target buffer
> - * @buflen: target buffer length
> - *
> - * Format the path of the cgroup of @blkg into @buf.
> - */
> -static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
> -{
> - return cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
> -}
> -
> /**
> * blkg_get - get a blkg reference
> * @blkg: blkg to get
> --
> 2.39.2
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
