From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH v8 8/8] writeback, cgroup: release dying cgwbs by switching attached inodes Date: Tue, 8 Jun 2021 10:54:58 +0200 Message-ID: <20210608085458.GC5562@quack2.suse.cz> References: <20210608013123.1088882-1-guro@fb.com> <20210608013123.1088882-9-guro@fb.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1623142498; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=s57GF5EVrU8EkU6hVgTxTv92JSfKxB+kZ8XzRaWUnBM=; b=dMUn34jq76iZfpe+e/UvfR64NqfiyE3bGkAnY7c5GBBn26baRgLDP3PSf/g+WNPP6nOAh3 wxNlk4Q/cxIYWdmJZh48684o9Ycgg0G8kmQFLnQFdkIYRoOluOboCH4yj01stu5xe6fkZw n3WP11Zr8PmwFcRZ/QM2wsIbAoeJNFY= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1623142498; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=s57GF5EVrU8EkU6hVgTxTv92JSfKxB+kZ8XzRaWUnBM=; b=QB67RQ6oO8NzzFxSr5nVeyP4+sAxevwN2dFw2I9h2gNFohGorTS0PXXTrCglCxi/x2Cy7D qc3kQ5g6XNatMDAQ== Content-Disposition: inline In-Reply-To: <20210608013123.1088882-9-guro@fb.com> List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Roman Gushchin Cc: Jan Kara , Tejun Heo , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Dennis Zhou , Dave Chinner , cgroups@vger.kernel.org On Mon 07-06-21 18:31:23, Roman Gushchin wrote: > Asynchronously try to release dying cgwbs by switching attached inodes > to the nearest living ancestor wb. It helps to get rid of per-cgroup > writeback structures themselves and of pinned memory and block cgroups, > which are significantly larger structures (mostly due to large per-cpu > statistics data). This prevents memory waste and helps to avoid > different scalability problems caused by large piles of dying cgroups. > > Reuse the existing mechanism of inode switching used for foreign inode > detection. To speed things up batch up to 115 inode switching in a > single operation (the maximum number is selected so that the resulting > struct inode_switch_wbs_context can fit into 1024 bytes). Because > every switching consists of two steps divided by an RCU grace period, > it would be too slow without batching. Please note that the whole > batch counts as a single operation (when increasing/decreasing > isw_nr_in_flight). This allows to keep umounting working (flush the > switching queue), however prevents cleanups from consuming the whole > switching quota and effectively blocking the frn switching. > > A cgwb cleanup operation can fail due to different reasons (e.g. not > enough memory, the cgwb has an in-flight/pending io, an attached inode > in a wrong state, etc). In this case the next scheduled cleanup will > make a new attempt. An attempt is made each time a new cgwb is offlined > (in other words a memcg and/or a blkcg is deleted by a user). In the > future an additional attempt scheduled by a timer can be implemented. > > Signed-off-by: Roman Gushchin > Acked-by: Tejun Heo > Acked-by: Dennis Zhou The patch looks good. Feel free to add: Reviewed-by: Jan Kara Just one codingstyle nit below. > + if (!wb_tryget(wb)) > + continue; > + > + spin_unlock_irq(&cgwb_lock); > + while ((cleanup_offline_cgwb(wb))) ^^ too many parentheses here... > + cond_resched(); > + spin_lock_irq(&cgwb_lock); Honza -- Jan Kara SUSE Labs, CR