linux-kernel - Re: [PATCH] Export current_is

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Date:	Wed, 6 Dec 2006 10:37:23 -0800 (PST)
From:	Linus Torvalds <torvalds@...l.org>
To:	David Howells <dhowells@...hat.com>
cc:	Andrew Morton <akpm@...l.org>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	Roland Dreier <rdreier@...co.com>,
	Andy Fleming <afleming@...escale.com>,
	Ben Collins <ben.collins@...ntu.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>, linux-arch@...r.kernel.org
Subject: Re: [PATCH] Export current_is_keventd() for libphy 



On Wed, 6 Dec 2006, Linus Torvalds wrote:
>
> and remove the "volatile" from all the bitop accessor functions.

It might also be interesting to see if this would change code-size at all. 

There's a number of things that check different bits in the same word 
right now, and they just reload the word unnecessarily and do multiple 
tests. Some of the page flags functions obviously already work around this 
by doing horrible things by hand instead, eg:

                (page->flags & (
                        1 << PG_lru     |
                        1 << PG_private |
                        1 << PG_locked  |
                        1 << PG_active  |
                        1 << PG_reclaim |
                        1 << PG_slab    |
                        1 << PG_swapcache |
                        1 << PG_writeback |
                        1 << PG_reserved |
                        1 << PG_buddy ))

in the free_pages_check() thing. It may make sense there, but we really 
_should_ allow gcc to just do things like this for us, and just use the 
proper functions to test bits.

			Linus
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