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[66.29.188.166]) by smtp.gmail.com with ESMTPSA id n22sm14673393pfh.166.2018.11.28.05.44.02 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 28 Nov 2018 05:44:04 -0800 (PST) Subject: Re: [PATCH V12 00/20] block: support multi-page bvec To: Ming Lei Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Theodore Ts'o , Omar Sandoval , Sagi Grimberg , Dave Chinner , Kent Overstreet , Mike Snitzer , dm-devel@redhat.com, Alexander Viro , linux-fsdevel@vger.kernel.org, Shaohua Li , linux-raid@vger.kernel.org, David Sterba , linux-btrfs@vger.kernel.org, "Darrick J . Wong" , linux-xfs@vger.kernel.org, Gao Xiang , Christoph Hellwig , linux-ext4@vger.kernel.org, Coly Li , linux-bcache@vger.kernel.org, Boaz Harrosh , Bob Peterson , cluster-devel@redhat.com References: <20181126021720.19471-1-ming.lei@redhat.com> From: Jens Axboe Message-ID: <7096bc4e-0617-29d0-a90d-ae7caf09a16d@kernel.dk> Date: Wed, 28 Nov 2018 06:44:00 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181126021720.19471-1-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/25/18 7:17 PM, Ming Lei wrote: > Hi, > > This patchset brings multi-page bvec into block layer: > > 1) what is multi-page bvec? > > Multipage bvecs means that one 'struct bio_bvec' can hold multiple pages > which are physically contiguous instead of one single page used in linux > kernel for long time. > > 2) why is multi-page bvec introduced? > > Kent proposed the idea[1] first. > > As system's RAM becomes much bigger than before, and huge page, transparent > huge page and memory compaction are widely used, it is a bit easy now > to see physically contiguous pages from fs in I/O. On the other hand, from > block layer's view, it isn't necessary to store intermediate pages into bvec, > and it is enough to just store the physicallly contiguous 'segment' in each > io vector. > > Also huge pages are being brought to filesystem and swap [2][6], we can > do IO on a hugepage each time[3], which requires that one bio can transfer > at least one huge page one time. Turns out it isn't flexiable to change > BIO_MAX_PAGES simply[3][5]. Multipage bvec can fit in this case very well. > As we saw, if CONFIG_THP_SWAP is enabled, BIO_MAX_PAGES can be configured > as much bigger, such as 512, which requires at least two 4K pages for holding > the bvec table. I'm pretty happy with this patchset at this point, looks like it just needs a respin to address the last comments. My only concern is whether it's a good idea to target this for 4.21, or if we should wait until 4.22. 4.21 has a fairly substantial amount of changes in terms of block already, it's not the best timing for something of this magnitude too. I'm going back and forth on those one a bit. Any concerns with pushing this to 4.22? -- Jens Axboe