From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 40546C282C4 for ; Sat, 9 Feb 2019 09:48:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 137F8217D8 for ; Sat, 9 Feb 2019 09:48:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726832AbfBIJs3 (ORCPT ); Sat, 9 Feb 2019 04:48:29 -0500 Received: from mx2.suse.de ([195.135.220.15]:54510 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726058AbfBIJs3 (ORCPT ); Sat, 9 Feb 2019 04:48:29 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id CA847AFDC; Sat, 9 Feb 2019 09:48:27 +0000 (UTC) Subject: Re: [PATCH 12/19] io_uring: add support for pre-mapped user IO buffers To: Jens Axboe , linux-aio@kvack.org, linux-block@vger.kernel.org, linux-api@vger.kernel.org Cc: hch@lst.de, jmoyer@redhat.com, avi@scylladb.com, jannh@google.com, viro@ZenIV.linux.org.uk References: <20190208173423.27014-1-axboe@kernel.dk> <20190208173423.27014-13-axboe@kernel.dk> From: Hannes Reinecke Message-ID: <263c8879-76c7-fd53-d37d-68b2e6993a9b@suse.de> Date: Sat, 9 Feb 2019 10:48:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20190208173423.27014-13-axboe@kernel.dk> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2/8/19 6:34 PM, Jens Axboe wrote: > If we have fixed user buffers, we can map them into the kernel when we > setup the io_uring. That avoids the need to do get_user_pages() for > each and every IO. > > To utilize this feature, the application must call io_uring_register() > after having setup an io_uring instance, passing in > IORING_REGISTER_BUFFERS as the opcode. The argument must be a pointer to > an iovec array, and the nr_args should contain how many iovecs the > application wishes to map. > > If successful, these buffers are now mapped into the kernel, eligible > for IO. To use these fixed buffers, the application must use the > IORING_OP_READ_FIXED and IORING_OP_WRITE_FIXED opcodes, and then > set sqe->index to the desired buffer index. sqe->addr..sqe->addr+seq->len > must point to somewhere inside the indexed buffer. > > The application may register buffers throughout the lifetime of the > io_uring instance. It can call io_uring_register() with > IORING_UNREGISTER_BUFFERS as the opcode to unregister the current set of > buffers, and then register a new set. The application need not > unregister buffers explicitly before shutting down the io_uring > instance. > > It's perfectly valid to setup a larger buffer, and then sometimes only > use parts of it for an IO. As long as the range is within the originally > mapped region, it will work just fine. > > For now, buffers must not be file backed. If file backed buffers are > passed in, the registration will fail with -1/EOPNOTSUPP. This > restriction may be relaxed in the future. > > RLIMIT_MEMLOCK is used to check how much memory we can pin. A somewhat > arbitrary 1G per buffer size is also imposed. > > Signed-off-by: Jens Axboe > --- > arch/x86/entry/syscalls/syscall_32.tbl | 1 + > arch/x86/entry/syscalls/syscall_64.tbl | 1 + > fs/io_uring.c | 356 ++++++++++++++++++++++++- > include/linux/sched/user.h | 2 +- > include/linux/syscalls.h | 2 + > include/uapi/asm-generic/unistd.h | 4 +- > include/uapi/linux/io_uring.h | 13 +- > kernel/sys_ni.c | 1 + > 8 files changed, 363 insertions(+), 17 deletions(-) > Reviewed-by: Hannes Reinecke Cheers, Hannes