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Fri, 21 Aug 2020 21:21:06 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Fri, 21 Aug 2020 21:21:06 -0700 Received: from HQMAIL111.nvidia.com (172.20.187.18) by HQMAIL109.nvidia.com (172.20.187.15) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Sat, 22 Aug 2020 04:21:05 +0000 Received: from hqnvemgw03.nvidia.com (10.124.88.68) by HQMAIL111.nvidia.com (172.20.187.18) with Microsoft SMTP Server (TLS) id 15.0.1473.3 via Frontend Transport; Sat, 22 Aug 2020 04:21:05 +0000 Received: from sandstorm.nvidia.com (Not Verified[10.2.94.162]) by hqnvemgw03.nvidia.com with Trustwave SEG (v7,5,8,10121) id ; Fri, 21 Aug 2020 21:21:05 -0700 From: John Hubbard To: Andrew Morton CC: Alexander Viro , Christoph Hellwig , Ilya Dryomov , Jens Axboe , Jeff Layton , , , , , , LKML , John Hubbard Subject: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast() Date: Fri, 21 Aug 2020 21:20:54 -0700 Message-ID: <20200822042059.1805541-1-jhubbard@nvidia.com> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 X-NVConfidentiality: public DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1598069950; bh=iXBAhlDsGHGJ0BL2z0xZCdQ0KPj09q9n3S14YFuk7Lw=; h=X-PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer: MIME-Version:X-NVConfidentiality:Content-Transfer-Encoding: Content-Type; b=CR22qrcQtjZToR+Y4AXxJBXCfRczkFv9gLGIEHhDFMLUu4lf6rgLvtPhciCvG0fvf 8JMCctIFdDTWGAzXzUKbKnyYt6PwVt10412J6p/kV+Y0t4d87XeRWNvV7rAJ2JgP31 d/5x/ygntRNdZv7aMmnGbKeHHcc0OCfwjSwvgZMX+1lVs78tO1hDzy8fykG7Hz3ok1 mw6vWF1LW8LjO7d+e41OQ4iw21XaLGKwEc023ZXuR+EN1hRFez1kp1TmDXy5s91Yv8 Yy8oSMjNVP/9FDFofUWl7D5rayjXLwB32kN+Y8cF+l0u4qTOBIqNxYvbqe1Xo9DjGq kGQPDLQF/puTQ== X-Rspamd-Queue-Id: A792A1ACEBC X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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: Hi, This converts the Direct IO block/bio layer over to use FOLL_PIN pages (those acquired via pin_user_pages*()). This effectively converts several file systems (ext4, for example) that use the common Direct IO routines. See "Remaining work", below for a bit more detail there. Quite a few approaches have been considered over the years. This one is inspired by Christoph Hellwig's July, 2019 observation that there are only 5 ITER_ types, and we can simplify handling of them for Direct IO [1]. After working through how bio submission and completion works, I became convinced that this is the simplest and cleanest approach to conversion. Not content to let well enough alone, I then continued on to the unthinkable: adding a new flag to struct bio, whose "short int" flags field was full, thuse triggering an expansion of the field from 16, to 32 bits. This allows for a nice assertion in bio_release_pages(), that the bio page release mechanism matches the page acquisition mechanism. This is especially welcome for a change that affects a lot of callers and could really make a mess if there is a bug somewhere. I'm unable to spot any performance implications, either theoretically or via (rather light) performance testing, from enlarging bio.bi_flags, but I suspect that there are maybe still valid reasons for having such a tiny bio.bi_flags field. I just have no idea what they are. (Hardware that knows the size of a bio? No, because there would be obvious build-time assertions, and comments about such a constraint.) Anyway, I can drop that patch if it seems like too much cost for too little benefit. And finally, as long as we're all staring at the iter_iov code, I'm including a nice easy ceph patch, that removes one more caller of iter_iov_get_pages(). Design notes ============ This whole approach depends on certain concepts: 1) Each struct bio instance must not mix different types of pages: FOLL_PIN and non-FOLL_PIN pages. (By FOLL_PIN I'm referring to pages that were acquired and pinned via pin_user_page*() routines.) Fortunately, this is already an enforced constraint for bio's, as evidenced by the existence and use of BIO_NO_PAGE_REF. 2) Christoph Hellwig's July, 2019 observation that there are only 5 ITER_ types, and we can simplify handling of them for Direct IO [1]. Accordingly, this series implements the following pseudocode: Direct IO behavior: ITER_IOVEC: pin_user_pages_fast(); break; ITER_KVEC: // already elevated page refcount, leave alone ITER_BVEC: // already elevated page refcount, leave alone ITER_PIPE: // just, no :) ITER_DISCARD: // discard return -EFAULT or -ENVALID; ...which works for callers that already have sorted out which case they are in. Such as, Direct IO in the block/bio layers. Now, this does leave ITER_KVEC and ITER_BVEC unconverted, but on the other hand, it's not clear that these are actually affected in the real world, by the get_user_pages()+filesystem interaction problems of [2]. If it turns out to matter, then those can be handled too, but it's just more refactoring and surgery to do so. Testing ======= Performance: no obvious regressions from running fio (direct=1: Direct IO) on both SSD and NVMe drives. Functionality: selected non-destructive bare metal xfstests on xfs, ext4, btrfs, orangefs filesystems, plus LTP tests. Note that I have only a single x86 64-bit test machine, though. Remaining work ============== Non-converted call sites for iter_iov_get_pages*() at the moment include: net, crypto, cifs, ceph, vhost, fuse, nfs/direct, vhost/scsi. About-to-be-converted sites (in a subsequent patch) are: Direct IO for filesystems that use the generic read/write functions. [1] https://lore.kernel.org/kvm/20190724061750.GA19397@infradead.org/ [2] "Explicit pinning of user-space pages": https://lwn.net/Articles/807108/ John Hubbard (5): iov_iter: introduce iov_iter_pin_user_pages*() routines mm/gup: introduce pin_user_page() bio: convert get_user_pages_fast() --> pin_user_pages_fast() bio: introduce BIO_FOLL_PIN flag fs/ceph: use pipe_get_pages_alloc() for pipe block/bio.c | 29 +++++++------ block/blk-map.c | 7 +-- fs/ceph/file.c | 3 +- fs/direct-io.c | 30 ++++++------- fs/iomap/direct-io.c | 2 +- include/linux/blk_types.h | 5 ++- include/linux/mm.h | 2 + include/linux/uio.h | 9 +++- lib/iov_iter.c | 91 +++++++++++++++++++++++++++++++++++++-- mm/gup.c | 30 +++++++++++++ 10 files changed, 169 insertions(+), 39 deletions(-)