linux-kernel - Re: [RFC v3 0/4] vfs: Non-blockling buffered fs read (page cache only)

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Message-ID: <20140925111655.GA8169@quack.suse.cz>
Date:	Thu, 25 Sep 2014 13:16:55 +0200
From:	Jan Kara <jack@...e.cz>
To:	Michael Kerrisk <mtk.manpages@...il.com>
Cc:	Milosz Tanski <milosz@...in.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-aio <linux-aio@...ck.org>, Mel Gorman <mgorman@...e.de>,
	Volker Lendecke <Volker.Lendecke@...net.de>,
	Tejun Heo <tj@...nel.org>, Jeff Moyer <jmoyer@...hat.com>,
	Theodore Ts'o <tytso@....edu>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [RFC v3 0/4] vfs: Non-blockling buffered fs read (page cache
 only)

On Thu 25-09-14 06:06:14, Michael Kerrisk wrote:
> Hello Milosz,
> 
> On Wed, Sep 24, 2014 at 11:46 PM, Milosz Tanski <milosz@...in.com> wrote:
> > This patcheset introduces an ability to perform a non-blocking read from
> > regular files in buffered IO mode. This works by only for those filesystems
> > that have data in the page cache.
> >
> > It does this by introducing new syscalls new syscalls preadv2/pwritev2. These
> > new syscalls behave like the network sendmsg, recvmsg syscalls that accept an
> > extra flag argument (RWF_NONBLOCK).
> >
> > It's a very common patern today (samba, libuv, etc..) use a large threadpool to
> > perform buffered IO operations. They submit the work form another thread
> > that performs network IO and epoll or other threads that perform CPU work. This
> > leads to increased latency for processing, esp. in the case of data that's
> > already cached in the page cache.
> >
> > With the new interface the applications will now be able to fetch the data in
> > their network / cpu bound thread(s) and only defer to a threadpool if it's not
> > there. In our own application (VLDB) we've observed a decrease in latency for
> > "fast" request by avoiding unnecessary queuing and having to swap out current
> > tasks in IO bound work threads.
> 
> Since this is a change to the user-space API, could you CC future
> versions of this patch set to linux-api@...rr.kernel.org please, as
  There's typo in the address. It should be:
linux-api@...r.kernel.org

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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