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Date: Tue, 25 Aug 2020 03:22:19 +0100 From: Al Viro <viro@...iv.linux.org.uk> To: John Hubbard <jhubbard@...dia.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Hellwig <hch@...radead.org>, Ilya Dryomov <idryomov@...il.com>, Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org, ceph-devel@...r.kernel.org, linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast() On Mon, Aug 24, 2020 at 07:07:02PM -0700, John Hubbard wrote: > On 8/24/20 6:54 PM, Al Viro wrote: > > On Fri, Aug 21, 2020 at 09:20:54PM -0700, John Hubbard wrote: > > > > > 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 :) > > > > Why? What's wrong with splice to O_DIRECT file? > > > > Oh! I'll take a look. Is this the fs/splice.c stuff? I ruled this out early > mainly based on Christoph's comment in [1] ("ITER_PIPE is rejected іn the > direct I/O path"), but if it's supportable then I'll hook it up. ; cat >a.c <<'EOF' #define _GNU_SOURCE #include <fcntl.h> #include <unistd.h> #include <stdlib.h> int main() { int fd = open("./a.out", O_DIRECT); splice(fd, NULL, 1, NULL, 4096, 0); return 0; } EOF ; cc a.c ; ./a.out | wc -c 4096 and you just had ->read_iter() called with ITER_PIPE destination.
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