linux-kernel - Re: [PATCH 07/13] writeback: explicit low bound for vm.dirty

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Message-Id: <20100809235652.7113.A69D9226@jp.fujitsu.com>
Date:	Tue, 10 Aug 2010 12:12:06 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>,
	Mel Gorman <mel@....ul.ie>,
	Chris Mason <chris.mason@...cle.com>,
	Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 07/13] writeback: explicit low bound for vm.dirty_ratio

> Subject: writeback: explicit low bound for vm.dirty_ratio
> From: Wu Fengguang <fengguang.wu@...el.com>
> Date: Thu Jul 15 10:28:57 CST 2010
> 
> Force a user visible low bound of 5% for the vm.dirty_ratio interface.
> 
> This is an interface change. When doing
> 
> 	echo N > /proc/sys/vm/dirty_ratio
> 
> where N < 5, the old behavior is pretend to accept the value, while
> the new behavior is to reject it explicitly with -EINVAL.  This will
> possibly break user space if they checks the return value.

Umm.. I dislike this change. Is there any good reason to refuse explicit 
admin's will? Why 1-4% is so bad? Internal clipping can be changed later
but explicit error behavior is hard to change later.

personally I prefer to
 - accept all value, or
 - clipping value in dirty_ratio_handler 

Both don't have explicit ABI change.

Thanks.



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