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Mon, 1 Feb 2021 03:08:29 +0000 (GMT) From: Changheun Lee To: nanich.lee@samsung.com Cc: Johannes.Thumshirn@wdc.com, asml.silence@gmail.com, axboe@kernel.dk, damien.lemoal@wdc.com, hch@infradead.org, jisoo2146.oh@samsung.com, junho89.kim@samsung.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, ming.lei@redhat.com, mj0123.lee@samsung.com, osandov@fb.com, patchwork-bot@kernel.org, seunghwan.hyun@samsung.com, sookwan7.kim@samsung.com, tj@kernel.org, tom.leiming@gmail.com, woosung2.lee@samsung.com, yt0928.kim@samsung.com Subject: Re: [PATCH v4 1/2] bio: limit bio max size Date: Mon, 1 Feb 2021 11:52:48 +0900 Message-Id: <20210201025248.17679-1-nanich.lee@samsung.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20210129034909.18785-1-nanich.lee@samsung.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFrrLJsWRmVeSWpSXmKPExsWy7bCmru76AvEEg01zWS3mrNrGaLH6bj+b RWv7NyaL0xMWMVn0PGlitfjbdY/J4uvDYou9t7QtLu+aw2ZxaHIzk8X0zXOYLa7dP8Nucfje VRaLh0smMlucO/mJ1WLeYweLX8uPMlq8/3Gd3eLUjsnMFuv3/mRzEPGY2PyO3WPnrLvsHptX aHlcPlvqsWlVJ5vH+31X2Tz6tqxi9Pi8Sc6j/UA3UwBnVI5NRmpiSmqRQmpecn5KZl66rZJ3 cLxzvKmZgaGuoaWFuZJCXmJuqq2Si0+ArltmDtBbSgpliTmlQKGAxOJiJX07m6L80pJUhYz8 4hJbpdSClJwCQ4MCveLE3OLSvHS95PxcK0MDAyNToMqEnIy1794xFXyVqLj/7SlbA2M7fxcj B4eEgInEqeOGXYxcHEICOxglJhx+w9rFyAnkfGKUWLZVGyLxjVGisX8iWAKkYee8BcwQib2M EicPPGSCcD4zSqy9s5kdpIpNQEei7+0tNhBbREBKYsvjlywgRcwCF5glDk28xwiyW1jAWGLq GhkQk0VAVWLG1xCQcl4Ba4m1u/5DLZOXeNq7nBnE5hSwkbi5YB4jRI2gxMmZT1hAbGagmuat s8EOkhB4wCGxsP0OG0Szi8SjRWugBglLvDq+hR3ClpJ42d/GDtHQzSjR3DafEcKZwCix5Pky JogqY4lPnz+DHcosoCmxfpc+RFhRYufvuYwQm/kk3n3tYYWEI69ER5sQRImKxJmW+8wwu56v 3Qk10UPizMKzjJDA6meUWHjrDeMERoVZSB6aheShWQibFzAyr2IUSy0ozk1PLTYsMEaO4U2M 4HSuZb6DcdrbD3qHGJk4GA8xSnAwK4nwnpokliDEm5JYWZValB9fVJqTWnyI0RQY2hOZpUST 84EZJa8k3tDUyNjY2MLEzNzM1FhJnDfJ4EG8kEB6YklqdmpqQWoRTB8TB6dUA9OjC8kGW0X4 tA5p/JbOS5Mx2rKz1f609z2DdZrrfzFunMfyf4Nd4ay5G6TPsH0/1CJzyM3XQ3OxnA2PZsaP RZ3rma8dEBZlXiI4SY9P1snWNjz9hvTBzJYZ3zk2b7SerLX6sCvHkyNrLpyo+lEyQ7vlzYW2 ijdxDJ5nTrplR+7fJN8zR232BkfN/xtcmbtFPJ8Xx+1duiKk/IPJsfrz5y5/1PGf1vi+iTfE PWnfZUnepTM0blpM4P57ykJM1HfW/q5+7a7VgWrrGqu3CjbmhGxh31/LfmVaZqniAXnJJVoW k12vztXPS91cKn2E70te4FH2zFqjSymhwj2r3m8LN34+defH4PJwoQw5ThOF80osxRmJhlrM RcWJAI9ZTU1wBAAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprCIsWRmVeSWpSXmKPExsWy7bCSnO7aAvEEg7sH+SzmrNrGaLH6bj+b RWv7NyaL0xMWMVn0PGlitfjbdY/J4uvDYou9t7QtLu+aw2ZxaHIzk8X0zXOYLa7dP8Nucfje VRaLh0smMlucO/mJ1WLeYweLX8uPMlq8/3Gd3eLUjsnMFuv3/mRzEPGY2PyO3WPnrLvsHptX aHlcPlvqsWlVJ5vH+31X2Tz6tqxi9Pi8Sc6j/UA3UwBnFJdNSmpOZllqkb5dAlfG2nfvmAq+ SlTc//aUrYGxnb+LkZNDQsBEYue8BcxdjFwcQgK7GSUWXZvCDpGQkjh+4i1rFyMHkC0scfhw MUTNR0aJR/d62UBq2AR0JPre3gKzRYDqtzx+yQJSxCzwglnixfcbzCDNwgLGElPXyICYLAKq EjO+hoCU8wpYS6zd9Z8VYpW8xNPe5cwgNqeAjcTNBfMYQcqFgGq+PdKCKBeUODnzCQuIzQxU 3rx1NvMERoFZSFKzkKQWMDKtYpRMLSjOTc8tNiwwzEst1ytOzC0uzUvXS87P3cQIjjgtzR2M 21d90DvEyMTBeIhRgoNZSYT31CSxBCHelMTKqtSi/Pii0pzU4kOM0hwsSuK8F7pOxgsJpCeW pGanphakFsFkmTg4pRqYVD3Tgpi1nxdUG0VwTQr+s2aNc9eD5W1OBd9+P7rxb6/w3KmqMxv8 fpx0YHz0V+YS6xXG7x3ZvmXHNaeFp8lw9AetnSmuMmPmqsAXF17pmXKu+sR791eb1p5U24lr HwWIzd4QvCq3/Z3Azye5IgXnruspz1Rnep1eOHmT0LzNRoETXQ7ar0k8WtC0eGnZ51xuJe9f v80r7nd/CbY3nyqgdGjfMqO9tzVWKScsFG5cm6u285vNdJVciV1TMnpyg9vytE8qXKsofbXh mOmNa9u3CcXxfK45Ijk/XOva5BuswXuCNlc+mnzzY0lXaJ3MI4PbU/tlawIrDBZlT5e6wuGd 46P8Pl+WR2ft5Y77P7PklViKMxINtZiLihMB1sDmxCcDAAA= X-CMS-MailID: 20210201030830epcas1p402e8a088fb16af9fbbb130b152e097f1 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-Sendblock-Type: SVC_REQ_APPROVE CMS-TYPE: 101P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20210201030830epcas1p402e8a088fb16af9fbbb130b152e097f1 References: <20210129034909.18785-1-nanich.lee@samsung.com> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org > On Fri, Jan 29, 2021 at 12:49:08PM +0900, Changheun Lee wrote: > > bio size can grow up to 4GB when muli-page bvec is enabled. > > but sometimes it would lead to inefficient behaviors. > > in case of large chunk direct I/O, - 32MB chunk read in user space - > > all pages for 32MB would be merged to a bio structure if the pages > > physical addresses are contiguous. it makes some delay to submit > > until merge complete. bio max size should be limited to a proper size. > > > > When 32MB chunk read with direct I/O option is coming from userspace, > > kernel behavior is below now. it's timeline. > > > > | bio merge for 32MB. total 8,192 pages are merged. > > | total elapsed time is over 2ms. > > |------------------ ... ----------------------->| > > | 8,192 pages merged a bio. > > | at this time, first bio submit is done. > > | 1 bio is split to 32 read request and issue. > > |---------------> > > |---------------> > > |---------------> > > ...... > > |---------------> > > |--------------->| > > total 19ms elapsed to complete 32MB read done from device. | > > > > If bio max size is limited with 1MB, behavior is changed below. > > > > | bio merge for 1MB. 256 pages are merged for each bio. > > | total 32 bio will be made. > > | total elapsed time is over 2ms. it's same. > > | but, first bio submit timing is fast. about 100us. > > |--->|--->|--->|---> ... -->|--->|--->|--->|--->| > > | 256 pages merged a bio. > > | at this time, first bio submit is done. > > | and 1 read request is issued for 1 bio. > > |---------------> > > |---------------> > > |---------------> > > ...... > > |---------------> > > |--------------->| > > total 17ms elapsed to complete 32MB read done from device. | > > Can you share us if enabling THP in your application can avoid this issue? BTW, you > need to make the 32MB buffer aligned with huge page size. IMO, THP perfectly fits > your case. > THP is enabled already like as below in my environment. It has no effect. cat /sys/kernel/mm/transparent_hugepage/enabled [always] madvise never This issue was reported from performance benchmark application in open market. I can't control application's working in open market. It's not only my own case. This issue might be occured in many mobile environment. At least, I checked this problem in exynos, and qualcomm chipset. > > Thanks, > Ming > > --- Changheun Lee Samsung Electronics.