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[109.152.100.135]) by smtp.gmail.com with ESMTPSA id i10sm5337446wrs.22.2020.11.20.05.03.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 20 Nov 2020 05:03:44 -0800 (PST) Subject: Re: [PATCH v2 1/2] iov_iter: optimise iov_iter_npages for bvec To: Matthew Wilcox , Christoph Hellwig Cc: Ming Lei , linux-fsdevel@vger.kernel.org, Alexander Viro , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20201120012017.GJ29991@casper.infradead.org> <35d5db17-f6f6-ec32-944e-5ecddcbcb0f1@gmail.com> <20201120022200.GB333150@T590> <20201120025457.GM29991@casper.infradead.org> <20201120081429.GA30801@infradead.org> <20201120123931.GN29991@casper.infradead.org> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Message-ID: Date: Fri, 20 Nov 2020 13:00:37 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20201120123931.GN29991@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/11/2020 12:39, Matthew Wilcox wrote: > On Fri, Nov 20, 2020 at 08:14:29AM +0000, Christoph Hellwig wrote: >> On Fri, Nov 20, 2020 at 02:54:57AM +0000, Matthew Wilcox wrote: >>> On Fri, Nov 20, 2020 at 02:25:08AM +0000, Pavel Begunkov wrote: >>>> On 20/11/2020 02:22, Ming Lei wrote: >>>>> iov_iter_npages(bvec) still can be improved a bit by the following way: >>>> >>>> Yep, was doing exactly that, +a couple of other places that are in my way. >>> >>> Are you optimising the right thing here? Assuming you're looking at >>> the one in do_blockdev_direct_IO(), wouldn't we be better off figuring >>> out how to copy the bvecs directly from the iov_iter into the bio >>> rather than calling dio_bio_add_page() for each page? >> >> Which is most effectively done by stopping to to use *blockdev_direct_IO >> and switching to iomap instead :) > > But iomap still calls iov_iter_npages(). So maybe we need something like > this ... Yep, all that are not mutually exclusive optimisations. Why `return 1`? It seems to be used later in bio_alloc(nr_pages) > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c > index 933f234d5bec..1c5a802a45d9 100644 > --- a/fs/iomap/direct-io.c > +++ b/fs/iomap/direct-io.c > @@ -250,7 +250,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length, > orig_count = iov_iter_count(dio->submit.iter); > iov_iter_truncate(dio->submit.iter, length); > > - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES); > + nr_pages = bio_iov_iter_npages(dio->submit.iter); > if (nr_pages <= 0) { > ret = nr_pages; > goto out; > @@ -308,7 +308,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length, > dio->size += n; > copied += n; > > - nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES); > + nr_pages = bio_iov_iter_npages(dio->submit.iter); > iomap_dio_submit_bio(dio, iomap, bio, pos); > pos += n; > } while (nr_pages); > diff --git a/include/linux/bio.h b/include/linux/bio.h > index c6d765382926..86cc74f84b30 100644 > --- a/include/linux/bio.h > +++ b/include/linux/bio.h > @@ -10,6 +10,7 @@ > #include > /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */ > #include > +#include > > #define BIO_DEBUG > > @@ -447,6 +448,16 @@ bool __bio_try_merge_page(struct bio *bio, struct page *page, > void __bio_add_page(struct bio *bio, struct page *page, > unsigned int len, unsigned int off); > int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter); > + > +static inline int bio_iov_iter_npages(const struct iov_iter *i) > +{ > + if (!iov_iter_count(i)) > + return 0; > + if (iov_iter_is_bvec(i)) > + return 1; > + return iov_iter_npages(i, BIO_MAX_PAGES); > +} > + > void bio_release_pages(struct bio *bio, bool mark_dirty); > extern void bio_set_pages_dirty(struct bio *bio); > extern void bio_check_pages_dirty(struct bio *bio); > -- Pavel Begunkov