From: Christopher Lameter <cl@linux.com>
To: Dave Chinner <david@fromorbit.com>
Cc: john.hubbard@gmail.com, Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Al Viro <viro@zeniv.linux.org.uk>,
Christian Benvenuti <benve@cisco.com>,
Christoph Hellwig <hch@infradead.org>,
Dan Williams <dan.j.williams@intel.com>,
Dennis Dalessandro <dennis.dalessandro@intel.com>,
Doug Ledford <dledford@redhat.com>,
Ira Weiny <ira.weiny@intel.com>, Jan Kara <jack@suse.cz>,
Jason Gunthorpe <jgg@ziepe.ca>,
Jerome Glisse <jglisse@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@kernel.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Mike Marciniszyn <mike.marciniszyn@intel.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Tom Talpey <tom@talpey.com>, LKML <linux-kernel@vger.kernel.org>,
linux-fsdevel@vger.kernel.org,
John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH v3 0/1] mm: introduce put_user_page*(), placeholder versions
Date: Tue, 12 Mar 2019 05:23:21 +0000 [thread overview]
Message-ID: <01000169705aecf0-76f2b83d-ac18-4872-9421-b4b6efe19fc7-000000@email.amazonses.com> (raw)
In-Reply-To: <20190310224742.GK26298@dastard>
On Mon, 11 Mar 2019, Dave Chinner wrote:
> > Direct IO on a mmapped file backed page doesnt make any sense.
>
> People have used it for many, many years as zero-copy data movement
> pattern. i.e. mmap the destination file, use direct IO to DMA direct
> into the destination file page cache pages, fdatasync() to force
> writeback of the destination file.
Well we could make that more safe through a special API that designates a
range of pages in a file in the same way as for RDMA. This is inherently
not reliable as we found out.
> Now we have copy_file_range() to optimise this sort of data
> movement, the need for games with mmap+direct IO largely goes away.
> However, we still can't just remove that functionality as it will
> break lots of random userspace stuff...
It is already broken and unreliable. Are there really "lots" of these
things around? Can we test this by adding a warning in the kernel and see
where it actually crops up?
next prev parent reply other threads:[~2019-03-12 5:23 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-06 23:54 john.hubbard
2019-03-06 23:54 ` [PATCH v3 1/1] " john.hubbard
2019-03-08 2:58 ` Christopher Lameter
2019-03-08 3:15 ` John Hubbard
2019-03-08 17:43 ` Weiny, Ira
2019-03-08 17:57 ` Jerome Glisse
2019-03-08 21:27 ` John Hubbard
2019-03-12 15:30 ` Ira Weiny
2019-03-13 0:38 ` John Hubbard
2019-03-13 14:49 ` Ira Weiny
2019-03-14 3:19 ` John Hubbard
2019-03-07 8:37 ` [PATCH v3 0/1] " Ira Weiny
2019-03-08 3:08 ` Christopher Lameter
2019-03-08 19:07 ` Jerome Glisse
2019-03-12 4:52 ` Christopher Lameter
2019-03-12 15:35 ` Jerome Glisse
2019-03-12 15:53 ` Jason Gunthorpe
2019-03-13 19:16 ` Christopher Lameter
2019-03-13 19:33 ` Jerome Glisse
2019-03-14 9:03 ` Jan Kara
2019-03-14 12:57 ` Jason Gunthorpe
2019-03-14 13:30 ` Jan Kara
2019-03-14 20:25 ` William Kucharski
2019-03-14 20:37 ` John Hubbard
2019-03-10 22:47 ` Dave Chinner
2019-03-12 5:23 ` Christopher Lameter [this message]
2019-03-12 10:39 ` Ira Weiny
2019-03-12 22:11 ` Dave Chinner
2019-03-12 15:23 ` Ira Weiny
2019-03-13 16:03 ` Christoph Hellwig
2019-03-13 19:21 ` Christopher Lameter
2019-03-14 9:06 ` Jan Kara
2019-03-18 20:12 ` John Hubbard
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