From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jan Kara <jack@suse.cz>
Subject: Re: [Lsf-pc] [LSF/MM TOPIC] async buffered diskio read for userspace
 apps
Date: Thu, 15 Jan 2015 23:31:57 +0100
Message-ID: <20150115223157.GB25884@quack.suse.cz>
References: <CANP1eJF77=iH_tm1y0CgF6PwfhUK6WqU9S92d0xAnCt=WhZVfQ@mail.gmail.com>
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Cc: lsf-pc@lists.linux-foundation.org,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	linux-mm@kvack.org, Christoph Hellwig <hch@infradead.org>
To: Milosz Tanski <milosz@adfin.com>
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On Thu 15-01-15 12:43:23, Milosz Tanski wrote:
> I would like to talk about enhancing the user interfaces for doing
> async buffered disk IO for userspace applications. There's a whole
> class of distributed web applications (most new applications today)
> that would benefit from such an API. Most of them today rely on
> cobbling one together in user space using a threadpool.
> 
> The current in kernel AIO interfaces that only support DIRECTIO, they
> were generally designed by and for big database vendors. The consensus
> is that the current AIO interfaces usually lead to decreased
> performance for those app.
> 
> I've been developing a new read syscall that allows non-blocking
> diskio read (provided that data is in the page cache). It's analogous
> to what exists today in the network world with recvmsg with MSG_NOWAIT
> flag. The work has been previously described by LWN here:
> https://lwn.net/Articles/612483/
> 
> Previous attempts (over the last 12+ years) at non-blocking buffered
> diskio has stalled due to their complexity. I would like to talk about
> the problem, my solution, and get feedback on the course of action.
> 
> Over the years I've been building the low level guys of various "web
> applications". That usually involves async network based applications
> (epoll based servers) and the biggest pain point for the last 8+ years
> has been async disk IO.
  Maybe this topic will be sorted out before LSF/MM. I know Andrew had some
objections about doc and was suggesting a solution using fincore() (which
Christoph refuted as being racy). Also there was a pending question
regarding whether the async read in this form will be used by applications.
But if it doesn't get sorted out a short session on the pending issues
would be probably useful.

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

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