linux-kernel - Re: [PATCH] mm: fix page_mkclean

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Message-ID: <Pine.LNX.4.64.0612280917000.4473@woody.osdl.org>
Date:	Thu, 28 Dec 2006 09:27:12 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	Russell King <rmk+lkml@....linux.org.uk>
cc:	Gordon Farquharson <gordonfarquharson@...il.com>,
	David Miller <davem@...emloft.net>, ranma@...edrich.de,
	tbm@...ius.com, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	andrei.popa@...eo.ro, Andrew Morton <akpm@...l.org>,
	hugh@...itas.com, nickpiggin@...oo.com.au, arjan@...radead.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: fix page_mkclean_one

On Thu, 28 Dec 2006, Russell King wrote:
> 
> and if you look at glibc's memset() function, you'll notice that's exactly
> what you expect if you pass a non-8bit value to it.  Ergo, what you're
> seeing is utterly expected given glibc's memset() implementation on ARM.

Guys, you _really_ should fix memset(). What you describe is a _bug_. 

"memset()" takes an "int" as its argument (always has), and has to convert 
it to a byte _itself_. It may not be common, but it's perfectly normal, to 
pass it values outside 0-255 (negative values that still fit in a "signed 
char" in particular are very normal, but my usage of "let the thing 
truncate it itself" is also quite fine).

> Fixing Linus' test program to pass nr & 255 to memset

No. I'm almost certain that that is not a "fix", it's a workaround for a 
serious bug in your glibc crap.

But it does explain all the unexpected strange behaviour (and the really 
small writeback size - now it doesn't need any /proc/sys/vm/dirty_ratio 
assumptions to be explicable.

		Linus
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