From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Leon Pollak <leon.pollak@gmail.com>, linux-kernel@vger.kernel.org
Subject: Re: Old O_DIRECT story
Date: Tue, 6 Jan 2015 04:04:45 +0200 [thread overview]
Message-ID: <20150106020445.GB23775@node.dhcp.inet.fi> (raw)
In-Reply-To: <20150105155210.4ac86388@lxorguk.ukuu.org.uk>
On Mon, Jan 05, 2015 at 03:52:10PM +0000, One Thousand Gnomes wrote:
> > I tried in all ways to implement this with mmap(), but it does not success,
> > because I did not find a way to mmap() file as O_WRONLY. Mapping as O_RDWR
> > makes kernel to pre-fill mapped memory with partition data. So, kernel and
> > DMA actually compete on the RAM area to fill it - one with garbage, one
> > with actual data. Kernel wins.
> >
> > So, how to implement Linus's advice?
>
> Use O_DIRECT. There are lots of problems with the mmap() model, in
> particular with how mmu table changes scale to large numbers of CPU
> threads (ie they don't).
They do. Kinda. See split page table lock.
But, yeah, mmap() approach should not be faster anyway.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2015-01-06 2:04 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-27 13:31 Old O_DIRECT story Leon Pollak
2014-12-27 16:08 ` Theodore Ts'o
2015-01-05 15:52 ` One Thousand Gnomes
2015-01-06 2:04 ` Kirill A. Shutemov [this message]
2015-01-06 7:53 ` Leon Pollak
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