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Date: Mon, 24 Aug 2020 19:13:27 -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 7:07 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
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