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[2603:800c:1a02:1bae:a7fa:157f:969a:4cde]) by smtp.gmail.com with ESMTPSA id s12-20020a63f04c000000b0047681fa88d1sm11161364pgj.53.2022.11.23.10.14.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Nov 2022 10:14:01 -0800 (PST) Sender: Tejun Heo Date: Wed, 23 Nov 2022 08:13:59 -1000 From: Tejun Heo To: Kemeng Shi Cc: josef@toxicpanda.com, axboe@kernel.dk, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 03/11] blk-throttle: ignore cgroup without io queued in blk_throtl_cancel_bios Message-ID: References: <20221123060401.20392-1-shikemeng@huawei.com> <20221123060401.20392-4-shikemeng@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221123060401.20392-4-shikemeng@huawei.com> X-Spam-Status: No, score=-1.6 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 23, 2022 at 02:03:53PM +0800, Kemeng Shi wrote: > Ignore cgroup without io queued in blk_throtl_cancel_bios for two > reasons: > 1. Save cpu cycle for trying to dispatch cgroup which is no io queued. > 2. Avoid non-consistent state that cgroup is inserted to service queue > without THROTL_TG_PENDING set as tg_update_disptime will unconditional > re-insert cgroup to service queue. If we are on the default hierarchy, > IO dispatched from child in tg_dispatch_one_bio will trigger inserting > cgroup to service queue without erase first and ruin the tree. > > Signed-off-by: Kemeng Shi > --- > block/blk-throttle.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > index b33bcf53b36e..acfac916ed99 100644 > --- a/block/blk-throttle.c > +++ b/block/blk-throttle.c > @@ -1728,7 +1728,12 @@ void blk_throtl_cancel_bios(struct gendisk *disk) > * Set the flag to make sure throtl_pending_timer_fn() won't > * stop until all throttled bios are dispatched. > */ > - blkg_to_tg(blkg)->flags |= THROTL_TG_CANCELING; > + tg->flags |= THROTL_TG_CANCELING; > + > + /* No need to dispatch cgroup without io queued */ It's probably more important to mention that putting this in without PENDING set can corrupt the tree in the future through double insertion. > + if (!(tg->flags & THROTL_TG_PENDING)) > + continue; > + Other than than the above comment, Acked-by: Tejun Heo Thanks. -- tejun