diff options
author | Dennis Zhou (Facebook) <dennisszhou@gmail.com> | 2018-09-11 21:41:28 +0300 |
---|---|---|
committer | Jens Axboe <axboe@kernel.dk> | 2018-09-22 05:29:05 +0300 |
commit | 07b05bcc3213ac9f8c28c9d835b4bf3d5798cc60 (patch) | |
tree | efab6cd44e334f64c1a98ae1b57a6894d9130c23 /block | |
parent | 49f4c2dc2b5066e9211101c59cc0828e81d41614 (diff) | |
download | linux-07b05bcc3213ac9f8c28c9d835b4bf3d5798cc60.tar.xz |
blkcg: convert blkg_lookup_create to find closest blkg
There are several scenarios where blkg_lookup_create can fail. Examples
include the blkcg dying, request_queue is dying, or simply being OOM. At
the end of the day, most handle this by simply falling back to the
q->root_blkg and calling it a day.
This patch implements the notion of closest blkg. During
blkg_lookup_create, if it fails to create, return the closest blkg
found or the q->root_blkg. blkg_try_get_closest is introduced and used
during association so a bio is always attached to a blkg.
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
-rw-r--r-- | block/bio.c | 17 | ||||
-rw-r--r-- | block/blk-cgroup.c | 25 |
2 files changed, 27 insertions, 15 deletions
diff --git a/block/bio.c b/block/bio.c index 083f1c9cde0a..bfd41e8b53a8 100644 --- a/block/bio.c +++ b/block/bio.c @@ -2007,21 +2007,24 @@ int bio_associate_blkcg(struct bio *bio, struct cgroup_subsys_state *blkcg_css) EXPORT_SYMBOL_GPL(bio_associate_blkcg); /** - * bio_associate_blkg - associate a bio with the specified blkg + * bio_associate_blkg - associate a bio with the a blkg * @bio: target bio * @blkg: the blkg to associate * - * Associate @bio with the blkg specified by @blkg. This is the queue specific - * blkcg information associated with the @bio, a reference will be taken on the - * @blkg and will be freed when the bio is freed. + * This tries to associate @bio with the specified blkg. Association failure + * is handled by walking up the blkg tree. Therefore, the blkg associated can + * be anything between @blkg and the root_blkg. This situation only happens + * when a cgroup is dying and then the remaining bios will spill to the closest + * alive blkg. + * + * A reference will be taken on the @blkg and will be released when @bio is + * freed. */ int bio_associate_blkg(struct bio *bio, struct blkcg_gq *blkg) { if (unlikely(bio->bi_blkg)) return -EBUSY; - if (!blkg_try_get(blkg)) - return -ENODEV; - bio->bi_blkg = blkg; + bio->bi_blkg = blkg_try_get_closest(blkg); return 0; } diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index cd0d97bed83d..e9e3a955f61a 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -268,9 +268,8 @@ err_free_blkg: * that all non-root blkg's have access to the parent blkg. This function * should be called under RCU read lock and @q->queue_lock. * - * Returns pointer to the looked up or created blkg on success, ERR_PTR() - * value on error. If @q is dead, returns ERR_PTR(-EINVAL). If @q is not - * dead and bypassing, returns ERR_PTR(-EBUSY). + * Returns the blkg or the closest blkg if blkg_create fails as it walks + * down from root. */ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg, struct request_queue *q) @@ -285,7 +284,7 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg, * we shouldn't allow anything to go through for a bypassing queue. */ if (unlikely(blk_queue_bypass(q))) - return ERR_PTR(blk_queue_dying(q) ? -ENODEV : -EBUSY); + return q->root_blkg; blkg = __blkg_lookup(blkcg, q, true); if (blkg) @@ -293,19 +292,29 @@ struct blkcg_gq *__blkg_lookup_create(struct blkcg *blkcg, /* * Create blkgs walking down from blkcg_root to @blkcg, so that all - * non-root blkgs have access to their parents. + * non-root blkgs have access to their parents. Returns the closest + * blkg to the intended blkg should blkg_create() fail. */ while (true) { struct blkcg *pos = blkcg; struct blkcg *parent = blkcg_parent(blkcg); - - while (parent && !__blkg_lookup(parent, q, false)) { + struct blkcg_gq *ret_blkg = q->root_blkg; + + while (parent) { + blkg = __blkg_lookup(parent, q, false); + if (blkg) { + /* remember closest blkg */ + ret_blkg = blkg; + break; + } pos = parent; parent = blkcg_parent(parent); } blkg = blkg_create(pos, q, NULL); - if (pos == blkcg || IS_ERR(blkg)) + if (IS_ERR(blkg)) + return ret_blkg; + if (pos == blkcg) return blkg; } } |