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[198.145.29.99]) by mx.google.com with ESMTPS id g127si3234668pgc.128.2019.07.23.13.07.30 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 23 Jul 2019 13:07:30 -0700 (PDT) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) client-ip=198.145.29.99; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=default header.b=VX9USo4G; spf=pass (google.com: domain of akpm@linux-foundation.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from akpm3.svl.corp.google.com (unknown [104.133.8.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0D4F32084D; Tue, 23 Jul 2019 20:07:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1563912450; bh=aJAwIMG/PcNFQKUZTnI3xqTnmOSc6qBWaaEdBvulUpA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VX9USo4Gy2dVgkf+TNz6HITq9P3GchWQKOUSzY/le0qD3BWAE3Fbfj7zdKjsmUOzb Dd1tT7mXRLQHqbUBmsJ2jqrXD2UEQHY2yKfHn0GeQXCYvKA/9zMzwnYY5F7fXbovHX FImaoH6ldCnadpDFM15AqXu4eNYu4RKODmNdv8DM= Date: Tue, 23 Jul 2019 13:07:29 -0700 From: Andrew Morton To: Konstantin Khlebnikov Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org, Tejun Heo , Jens Axboe , Johannes Weiner , Michal Hocko Subject: Re: [PATCH] mm/backing-dev: show state of all bdi_writeback in debugfs Message-Id: <20190723130729.522976a1f075d748fc946ff6@linux-foundation.org> In-Reply-To: <156388617236.3608.2194886130557491278.stgit@buzz> References: <156388617236.3608.2194886130557491278.stgit@buzz> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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: On Tue, 23 Jul 2019 15:49:32 +0300 Konstantin Khlebnikov wrote: > Currently /sys/kernel/debug/bdi/$maj:$min/stats shows only root bdi wb. > With CONFIG_CGROUP_WRITEBACK=y there is one for each memory cgroup. > > This patch shows here state of each bdi_writeback in form: > > > > Id: 1 > Cgroup: / > > > Id: xxx > Cgroup: /path > > > Id: yyy > Cgroup: /path2 > Why is this considered useful? What are the use cases. ie, why should we add this to Linux? > mm/backing-dev.c | 106 +++++++++++++++++++++++++++++++++++++++++++++++------- > 1 file changed, 93 insertions(+), 13 deletions(-) No documentation because it's debugfs, right? I'm struggling to understand why this is a good thing :(. If it's there and people use it then we should document it for them. If it's there and people don't use it then we should delete the code.