linux-kernel - Re: [PATCH -mmotm] mm: init_per_zone_pages_min - get rid of sqrt call on small machines

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Message-ID: <20090506064410.GB4865@lenovo>
Date:	Wed, 6 May 2009 10:44:10 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LMMML <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mmotm] mm: init_per_zone_pages_min - get rid of sqrt
	call on small machines

[David Rientjes - Tue, May 05, 2009 at 11:36:38PM -0700]
| On Wed, 6 May 2009, Cyrill Gorcunov wrote:
| 
| > Index: linux-2.6.git/mm/page_alloc.c
| > =====================================================================
| > --- linux-2.6.git.orig/mm/page_alloc.c
| > +++ linux-2.6.git/mm/page_alloc.c
| > @@ -4610,11 +4610,15 @@ static int __init init_per_zone_pages_mi
| >  
| >  	lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);
| >  
| > -	min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
| > -	if (min_free_kbytes < 128)
| > +	/* for small values we may eliminate sqrt operation completely */
| > +	if (lowmem_kbytes < 1024)
| >  		min_free_kbytes = 128;
| > -	if (min_free_kbytes > 65536)
| > -		min_free_kbytes = 65536;
| > +	else {
| > +		min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
| > +		if (min_free_kbytes > 65536)
| > +			min_free_kbytes = 65536;
| > +	}
| > +
| >  	setup_per_zone_pages_min();
| >  	setup_per_zone_lowmem_reserve();
| >  	setup_per_zone_inactive_ratio();
| 
| For a function that's called once, this just isn't worth it.  int_sqrt() 
| isn't expensive enough to warrant the assault on the readability of the 
| code.
| 

ok, then we could just drop it.

	-- Cyrill
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