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From: Al Viro <viro@zeniv.linux.org.uk>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@infradead.org>,
	Ilya Dryomov <idryomov@gmail.com>, Jens Axboe <axboe@kernel.dk>,
	Jeff Layton <jlayton@kernel.org>,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, ceph-devel@vger.kernel.org,
	linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast()
Date: Tue, 25 Aug 2020 03:22:19 +0100	[thread overview]
Message-ID: <20200825022219.GW1236603@ZenIV.linux.org.uk> (raw)
In-Reply-To: <3072d5a0-43c7-3396-c57f-6af83621b71c@nvidia.com>

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.

  reply	other threads:[~2020-08-25  2:22 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-22  4:20 John Hubbard
2020-08-22  4:20 ` [PATCH 1/5] iov_iter: introduce iov_iter_pin_user_pages*() routines John Hubbard
2020-08-22  4:20 ` [PATCH 2/5] mm/gup: introduce pin_user_page() John Hubbard
2020-08-22  4:20 ` [PATCH 3/5] bio: convert get_user_pages_fast() --> pin_user_pages_fast() John Hubbard
2020-08-22  4:20 ` [PATCH 4/5] bio: introduce BIO_FOLL_PIN flag John Hubbard
2020-08-23  6:25   ` Christoph Hellwig
2020-08-23  6:57     ` John Hubbard
2020-08-24  7:36       ` John Hubbard
2020-08-24  9:20     ` Jens Axboe
2020-08-24 14:42       ` Christoph Hellwig
2020-08-22  4:20 ` [PATCH 5/5] fs/ceph: use pipe_get_pages_alloc() for pipe John Hubbard
2020-08-24 10:53   ` Jeff Layton
2020-08-24 17:54     ` John Hubbard
2020-08-24 18:47       ` Jeff Layton
2020-08-24 18:54         ` Matthew Wilcox
2020-08-24 19:02           ` John Hubbard
2020-08-25  1:20           ` [PATCH v2] " John Hubbard
2020-08-25 16:22             ` Jeff Layton
2020-08-25  1:54 ` [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast() Al Viro
2020-08-25  2:07   ` Al Viro
2020-08-25  2:13     ` John Hubbard
2020-08-25  2:07   ` John Hubbard
2020-08-25  2:22     ` Al Viro [this message]
2020-08-25  2:27       ` John Hubbard

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