From nobody Fri Oct 17 10:32:20 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DDB0CC433FE for ; Wed, 19 Oct 2022 12:31:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233113AbiJSMbr (ORCPT ); Wed, 19 Oct 2022 08:31:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233033AbiJSMba (ORCPT ); Wed, 19 Oct 2022 08:31:30 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B6C09FADA; Wed, 19 Oct 2022 05:09:27 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E40E96174B; Wed, 19 Oct 2022 09:14:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EE72AC433D6; Wed, 19 Oct 2022 09:14:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1666170848; bh=pyFqEjCsJm/B3AhoMs/+9UBXpGWPBTmE33Qm6IaChXk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=HnFuyQ7qxqOnyY/uEjHDJq5Kv1sG9g0mbforwwHZdccwFChtanVBaFktGTzuC53fX JVbp2dLQtlflT8ujcul/ZWuq/KIYVPvu4wqUJ5Ov24r6O4i96+vxmipFkomnx3j9GV 4qbO2YqiQQ1oncqjdj6dPuen6P0xw+hVqCQyECdA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mingzhe Zou , Coly Li , Jens Axboe , Sasha Levin Subject: [PATCH 6.0 809/862] bcache: fix set_at_max_writeback_rate() for multiple attached devices Date: Wed, 19 Oct 2022 10:34:56 +0200 Message-Id: <20221019083325.659532040@linuxfoundation.org> X-Mailer: git-send-email 2.38.0 In-Reply-To: <20221019083249.951566199@linuxfoundation.org> References: <20221019083249.951566199@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Coly Li [ Upstream commit d2d05b88035d2d51a5bb6c5afec88a0880c73df4 ] Inside set_at_max_writeback_rate() the calculation in following if() check is wrong, if (atomic_inc_return(&c->idle_counter) < atomic_read(&c->attached_dev_nr) * 6) Because each attached backing device has its own writeback thread running and increasing c->idle_counter, the counter increates much faster than expected. The correct calculation should be, (counter / dev_nr) < dev_nr * 6 which equals to, counter < dev_nr * dev_nr * 6 This patch fixes the above mistake with correct calculation, and helper routine idle_counter_exceeded() is added to make code be more clear. Reported-by: Mingzhe Zou Signed-off-by: Coly Li Acked-by: Mingzhe Zou Link: https://lore.kernel.org/r/20220919161647.81238-6-colyli@suse.de Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/md/bcache/writeback.c | 73 +++++++++++++++++++++++++---------- 1 file changed, 52 insertions(+), 21 deletions(-) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 3f0ff3aab6f2..9c227e4a8465 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -157,6 +157,53 @@ static void __update_writeback_rate(struct cached_dev = *dc) dc->writeback_rate_target =3D target; } =20 +static bool idle_counter_exceeded(struct cache_set *c) +{ + int counter, dev_nr; + + /* + * If c->idle_counter is overflow (idel for really long time), + * reset as 0 and not set maximum rate this time for code + * simplicity. + */ + counter =3D atomic_inc_return(&c->idle_counter); + if (counter <=3D 0) { + atomic_set(&c->idle_counter, 0); + return false; + } + + dev_nr =3D atomic_read(&c->attached_dev_nr); + if (dev_nr =3D=3D 0) + return false; + + /* + * c->idle_counter is increased by writeback thread of all + * attached backing devices, in order to represent a rough + * time period, counter should be divided by dev_nr. + * Otherwise the idle time cannot be larger with more backing + * device attached. + * The following calculation equals to checking + * (counter / dev_nr) < (dev_nr * 6) + */ + if (counter < (dev_nr * dev_nr * 6)) + return false; + + return true; +} + +/* + * Idle_counter is increased every time when update_writeback_rate() is + * called. If all backing devices attached to the same cache set have + * identical dc->writeback_rate_update_seconds values, it is about 6 + * rounds of update_writeback_rate() on each backing device before + * c->at_max_writeback_rate is set to 1, and then max wrteback rate set + * to each dc->writeback_rate.rate. + * In order to avoid extra locking cost for counting exact dirty cached + * devices number, c->attached_dev_nr is used to calculate the idle + * throushold. It might be bigger if not all cached device are in write- + * back mode, but it still works well with limited extra rounds of + * update_writeback_rate(). + */ static bool set_at_max_writeback_rate(struct cache_set *c, struct cached_dev *dc) { @@ -167,21 +214,8 @@ static bool set_at_max_writeback_rate(struct cache_set= *c, /* Don't set max writeback rate if gc is running */ if (!c->gc_mark_valid) return false; - /* - * Idle_counter is increased everytime when update_writeback_rate() is - * called. If all backing devices attached to the same cache set have - * identical dc->writeback_rate_update_seconds values, it is about 6 - * rounds of update_writeback_rate() on each backing device before - * c->at_max_writeback_rate is set to 1, and then max wrteback rate set - * to each dc->writeback_rate.rate. - * In order to avoid extra locking cost for counting exact dirty cached - * devices number, c->attached_dev_nr is used to calculate the idle - * throushold. It might be bigger if not all cached device are in write- - * back mode, but it still works well with limited extra rounds of - * update_writeback_rate(). - */ - if (atomic_inc_return(&c->idle_counter) < - atomic_read(&c->attached_dev_nr) * 6) + + if (!idle_counter_exceeded(c)) return false; =20 if (atomic_read(&c->at_max_writeback_rate) !=3D 1) @@ -195,13 +229,10 @@ static bool set_at_max_writeback_rate(struct cache_se= t *c, dc->writeback_rate_change =3D 0; =20 /* - * Check c->idle_counter and c->at_max_writeback_rate agagain in case - * new I/O arrives during before set_at_max_writeback_rate() returns. - * Then the writeback rate is set to 1, and its new value should be - * decided via __update_writeback_rate(). + * In case new I/O arrives during before + * set_at_max_writeback_rate() returns. */ - if ((atomic_read(&c->idle_counter) < - atomic_read(&c->attached_dev_nr) * 6) || + if (!idle_counter_exceeded(c) || !atomic_read(&c->at_max_writeback_rate)) return false; =20 --=20 2.35.1