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Date: Mon, 24 Aug 2020 19:27:45 -0700 From: John Hubbard <jhubbard@...dia.com> To: Al Viro <viro@...iv.linux.org.uk> 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 8/24/20 7:22 PM, Al Viro wrote: > 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. > That example saves me a lot of time! Much appreciated. thanks, -- John Hubbard NVIDIA
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