From mboxrd@z Thu Jan 1 00:00:00 1970 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1184BCA0FED for ; Wed, 27 Aug 2025 18:58:26 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 49AB98E0005; Wed, 27 Aug 2025 14:58:25 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4727D8E0001; Wed, 27 Aug 2025 14:58:25 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3B0368E0005; Wed, 27 Aug 2025 14:58:25 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 2ABA28E0001 for ; Wed, 27 Aug 2025 14:58:25 -0400 (EDT) Received: from smtpin20.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id A38ECC07EF for ; Wed, 27 Aug 2025 18:58:24 +0000 (UTC) X-FDA: 83823448128.20.626E198 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf30.hostedemail.com (Postfix) with ESMTP id E72A78000E for ; Wed, 27 Aug 2025 18:58:22 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=J9dGK90d; spf=pass (imf30.hostedemail.com: domain of tj@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=tj@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1756321103; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=N62gBUQMd0tc7qQVo3b+XHms24SJjlkFbH+zkE6ad5I=; b=0J0EgJ0Kn8vskFXJaoR+7zAM74RnI4eevsdgqOKtUOVl2KsRDgGKe+E9+M1UD6sDzNJ4js krgMooT64IAIbjZGq9CEsMvCLQjgmKThNS62O90actYWVEkYxKnEq7ucEAqBkTnsnzT6JT 99pkZb7MpcfxrVdbnDoc5FX9zTAf87Y= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=J9dGK90d; spf=pass (imf30.hostedemail.com: domain of tj@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=tj@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1756321103; a=rsa-sha256; cv=none; b=TYds8Qsn3bf28PdihXThi67dWDY0xv5lhYZDj87Os4S+3yHb0kxLUpMcmAFHpEZJ3IIgQV an7uOErYEXkjhlunPo+ghNtcG95Ku326JZ4C9ZUcbBE2QOLkzqRQKCgt42yQ84MSfPkF/N otig19jPX77NI+KS1AcH4PZi04kWbhE= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id C230844441; Wed, 27 Aug 2025 18:58:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 821B0C4CEEB; Wed, 27 Aug 2025 18:58:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756321101; bh=5Gyv4X1Tqg+4AnDyOQUvhP/AeCmJe0OWG5RaUTEjY1o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=J9dGK90d9raYoU61eopREmg/6Q8VwGy1GFyM3/EiASEqRn32FBngL1hxSLw3SslED DYpM5Q4fCrJAuIPdeEsdXgaY2pFoRa8dmt9z9BgoMiVYul7fWta2pYVwzVQAeEfiPX fYrSLbBQ6xpchUjv6ZtNUIYJzuU1ChYSlvofjkOmemD0B+uOiul+cFjXiYFLWTIkIf QwI0cz3L7NPcBooRz9oV7+ko8EOmqvmdukO0xV4MlZbPLNbsS+EX2MHwEchquCeepo MFevgwQQiKMZpJa+iGp2o+rU/xXkjlxrDwP0xFzyvuH8hEG64D1Lzlf4Vpyvu9cOaD CLupkoqSIISOw== Date: Wed, 27 Aug 2025 08:58:20 -1000 From: Tejun Heo To: Julian Sun Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, jack@suse.cz, muchun.song@linux.dev Subject: Re: [PATCH v3] memcg: Don't wait writeback completion when release memcg. Message-ID: References: <20250827181356.40971-1-sunjunchao@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250827181356.40971-1-sunjunchao@bytedance.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: E72A78000E X-Stat-Signature: i9krp7cbp37ib5ft8yzkxtz1shefkyo4 X-Rspam-User: X-HE-Tag: 1756321102-478743 X-HE-Meta: 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 RJmvxmr9 uyGQfePGG+cSp8ZrKBnxIgByYlOGXMjPzFGkm/7i8nZXK3k0MmdbboXEiDpedkUgeFhYmwrYrqRrA90QDpn8YEi49/KnLMP746II5Gw58Ad+CCBefrzhGF71/zEZEhXLYkVp/AF3IUALaqBrYqe8ECONlB1R58QG8OI9Atqv9EU9Xam6VkOYcoXg0/vBuhbC/PGKooazcTK68UZIii6OZyllDMUjjUVw5NB2fJIHji+d1cCdCZdiAmPsdww== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hello, On Thu, Aug 28, 2025 at 02:13:56AM +0800, Julian Sun wrote: > diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h > index 2ad261082bba..6c1ed286da6a 100644 > --- a/include/linux/backing-dev-defs.h > +++ b/include/linux/backing-dev-defs.h > @@ -65,6 +65,13 @@ struct wb_completion { > wait_queue_head_t *waitq; > }; > > +static inline void wb_completion_init(struct wb_completion *done, > + struct wait_queue_head *waitq) Indentation. > +{ > + atomic_set(&done->cnt, 1); > + done->waitq = waitq; > +} > + > #define __WB_COMPLETION_INIT(_waitq) \ > (struct wb_completion){ .cnt = ATOMIC_INIT(1), .waitq = (_waitq) } > > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h > index 785173aa0739..24e881ce4909 100644 > --- a/include/linux/memcontrol.h > +++ b/include/linux/memcontrol.h > @@ -157,11 +157,17 @@ struct mem_cgroup_thresholds { > */ > #define MEMCG_CGWB_FRN_CNT 4 > > +struct cgwb_frn_wait { > + struct wb_completion done; > + struct wait_queue_entry wq_entry; > +}; > + > struct memcg_cgwb_frn { > u64 bdi_id; /* bdi->id of the foreign inode */ > int memcg_id; /* memcg->css.id of foreign inode */ > u64 at; /* jiffies_64 at the time of dirtying */ > - struct wb_completion done; /* tracks in-flight foreign writebacks */ > + struct wb_completion *done; /* tracks in-flight foreign writebacks */ > + struct cgwb_frn_wait *wait; /* used to free resources when release memcg */ Is ->done still needed? Can't it just do frn->wait.done? > +#ifdef CONFIG_CGROUP_WRITEBACK > +static int memcg_cgwb_waitq_callback_fn(struct wait_queue_entry *wq_entry, unsigned int mode, > + int flags, void *key) > +{ > + struct cgwb_frn_wait *frn_wait = container_of(wq_entry, > + struct cgwb_frn_wait, wq_entry); > + > + list_del(&wq_entry->entry); > + kfree(frn_wait); > + > + return 0; > +} > +#endif Note that the above will be called for all queued waits when any one entry triggers. It'd need to check whether done is zero before self-deleting and freeing. > @@ -3912,8 +3938,18 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css) > int __maybe_unused i; > > #ifdef CONFIG_CGROUP_WRITEBACK > - for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) > - wb_wait_for_completion(&memcg->cgwb_frn[i].done); > + for (i = 0; i < MEMCG_CGWB_FRN_CNT; i++) { > + struct memcg_cgwb_frn *frn = &memcg->cgwb_frn[i]; > + > + if (atomic_dec_and_test(&frn->done->cnt)) > + kfree(frn->wait); > + else > + /* > + * Not necessary to wait for wb completion which might cause task hung, > + * only used to free resources. See memcg_cgwb_waitq_callback_fn(). > + */ > + __add_wait_queue_entry_tail(frn->done->waitq, &frn->wait->wq_entry); > + } And then, this can probably be simplified to sth like: __add_wait_queue_entry_tail(...); if (atomic_dec_and_test(&frn->done->dnt); wake_up_all(waitq); Thanks. -- tejun