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

[Cyrill Gorcunov <gorcunov@gmail.com>]

[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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