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From: John Hubbard <jhubbard@nvidia.com>
To: Al Viro <viro@zeniv.linux.org.uk>
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: Mon, 24 Aug 2020 19:13:27 -0700	[thread overview]
Message-ID: <26bf92af-a7ab-b53f-45dd-9e3d7a1340ec@nvidia.com> (raw)
In-Reply-To: <20200825020700.GV1236603@ZenIV.linux.org.uk>

On 8/24/20 7:07 PM, Al Viro wrote:
> On Tue, Aug 25, 2020 at 02:54:28AM +0100, 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?
> 
> Sorry - s/to/from/, obviously.
> 
> To spell it out: consider generic_file_splice_read() behaviour when
> the source had been opened with O_DIRECT; you will get a call of
> ->read_iter() into ITER_PIPE destination.  And it bloody well
> will hit iov_iter_get_pages() on common filesystems, to pick the
> pages we want to read into.
> 
> So... what's wrong with having that "pin" primitive making sure
> the pages are there and referenced by the pipe?
> 

(our emails crossed) OK, yes, let me hook that up. I was just unaware
of that flow, I'll go off and figure it out.

Thanks for looking at this!

thanks,
-- 
John Hubbard
NVIDIA

  reply	other threads:[~2020-08-25  2:13 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 [this message]
2020-08-25  2:07   ` John Hubbard
2020-08-25  2:22     ` Al Viro
2020-08-25  2:27       ` John Hubbard

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