linux-kernel - Re: [RFC PATCH 0/7] Non-blockling buffered fs read (page cache only)

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Message-ID: <CANP1eJF_LjNVeD838D-H=005jtGTvGY=h5wPZBHfT6Z9iuKK_g@mail.gmail.com>
Date:	Tue, 16 Sep 2014 16:34:33 -0400
From:	Milosz Tanski <milosz@...in.com>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	linux-aio@...ck.org, Mel Gorman <mgorman@...e.de>,
	Volker Lendecke <Volker.Lendecke@...net.de>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH 0/7] Non-blockling buffered fs read (page cache only)

Jeff,

Which git repository do the man pages live in?

- Milosz

On Tue, Sep 16, 2014 at 3:30 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
> Milosz Tanski <milosz@...in.com> writes:
>
>> 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 readv2/writev2 and
>> preadv2/pwritev2. These new syscalls behave like the network sendmsg, recvmsg
>> syscalls that accept an extra flag argument (O_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.
>>
>> I have co-developed these changes with Christoph Hellwig, a whole lot of his
>> fixes went into the first patch in the series (were squashed with his
>> approval).
>>
>> I am going to post the perf report in a reply-to to this RFC.
>
> You can send the performance data along with the patch series, no need to
> separate it off in a reply.
>
> One additional patch I'd like to see is a man page update.  That would
> help clarify exactly what you're trying to accomplish.
>
> I look forward to v2!
>
> Cheers,
> Jeff



-- 
Milosz Tanski
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