From: Christoph Hellwig <hch@infradead.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: "Steinar H. Gunderson" <sesse@google.com>,
Christoph Hellwig <hch@infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [PATCH] Add support for usbfs zerocopy.
Date: Fri, 8 Jan 2016 01:45:35 -0800 [thread overview]
Message-ID: <20160108094535.GA17286@infradead.org> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1601061032000.1579-100000@iolanthe.rowland.org>
On Wed, Jan 06, 2016 at 10:35:05AM -0500, Alan Stern wrote:
> Indeed, the I/O operations we are using with mmap here are not reads or
> writes; they are ioctls. As far as I know, the kernel doesn't have any
> defined interface for zerocopy ioctls.
IF it was using mmap for I/O it would read in through the page fault
handler an then mark the page dirty for writeback by the VM. Thats
clearly not the case.
Instead it's using mmap on a file as a pecial purpose anonymous
memory allocator, bypassing the VM and VM policies, including
allowing to pin kernel memory that way.
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next parent reply other threads:[~2016-01-08 9:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20160106144512.GA21737@imap.gmail.com>
[not found] ` <Pine.LNX.4.44L0.1601061032000.1579-100000@iolanthe.rowland.org>
2016-01-08 9:45 ` Christoph Hellwig [this message]
2016-01-08 10:22 ` David Laight
2016-01-08 16:02 ` Oliver Neukum
2016-01-12 21:26 ` Steinar H. Gunderson
2016-01-12 22:05 ` Alan Stern
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