linux-kernel - Re: [patch] pipe: add support for shrinking and growing pipes

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Date:	Wed, 2 Jun 2010 21:25:52 +0200
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] pipe: add support for shrinking and growing pipes

On Tue, Jun 1, 2010 at 9:45 AM, Jens Axboe <axboe@...nel.dk> wrote:
> On Thu, May 27 2010, Michael Kerrisk wrote:
>> Jens,
>>
>> On Mon, May 24, 2010 at 7:56 PM, Jens Axboe <jens.axboe@...cle.com> wrote:
>> > On Mon, May 24 2010, Michael Kerrisk wrote:
>> >> On Mon, May 24, 2010 at 7:35 PM, Jens Axboe <jens.axboe@...cle.com> wrote:
>> >> > On Mon, May 24 2010, Michael Kerrisk wrote:
>> >> >> > Right, that looks like a thinko.
>> >> >> >
>> >> >> > I'll submit a patch changing it to bytes and the agreed API and fix this
>> >> >> > -Eerror. Thanks for your comments and suggestions!
>> >> >>
>> >> >> Thanks. And of course you are welcome. (Please CC linux-api@...r on
>> >> >> this patche (and all patches that change the API/ABI.)
>> >> >
>> >> > The first change is this:
>> >> >
>> >> > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=0191f8697bbdfefcd36e7b8dc3eeddfe82893e4b
>> >> >
>> >> > and the one dealing with the pages vs bytes API is this:
>> >> >
>> >> > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=b9598db3401282bb27b4aef77e3eee12015f7f29
>> >> >
>> >> > Not tested yet, will do so before sending in of course.
>> >>
>> >> Eyeballing it quickly, these changes look right.
>> >
>> > Good, thanks.
>> >
>> >> Do you have some test programs you can make available?
>> >
>> > Actually I don't, I test it by modifying fio's splice engine to set/get
>> > the pipe size and test the resulting transfers.
>>
>> An afterthought. Do there not also need to be fixes to the /proc
>> interfaces. I don't think they were included in your revised patches.
>
> I think the proc part can be sanely left in pages, since it's just a
> memory limiter.

I can't see any advantage to using two different units for these
closely related APIs, and it does seem like it could be a source of
confusion. Similar APIs that I can think of like RLIMIT_MEMLOCK and
shmget() SHMMAX that impose per-process memory-related limits use
bytes. Best to be consistent, don't you think?

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface" http://blog.man7.org/
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