linux-kernel - Re: [PATCH 02/22] Do not sanity check order in the fast path

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Date:	Thu, 23 Apr 2009 12:26:24 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 02/22] Do not sanity check order in the fast path

On Wed, 2009-04-22 at 18:34 -0700, Dave Hansen wrote:
> I'll also go and see what the actual .text size
> changes are from this patch both for alloc_pages() and
> alloc_pages_node() separately to make sure what we're dealing with
> here.  Does this check even *exist* in the optimized code very
> often?  

While this isn't definitive by any means, I did get some interesting
results.  Pulling the check out of alloc_pages() had no effect at *all*
on text size because I'm trying with CONFIG_NUMA=n.

$ size i386-T41-laptop.{0,1}/vmlinux
   text	   data	    bss	    dec	    hex	filename
4348625	 286560	 860160	5495345	 53da31	i386-T41-laptop.0/vmlinux
4348625	 286560	 860160	5495345	 53da31	i386-T41-laptop.1/vmlinux

We get a slightly different when pulling the check out of
alloc_pages_node():

$ size i386-T41-laptop.{1,2}/vmlinux
   text	   data	    bss	    dec	    hex	filename
4348625	 286560	 860160	5495345	 53da31	i386-T41-laptop.1/vmlinux
4348601	 286560	 860160	5495321	 53da19	i386-T41-laptop.2/vmlinux

$ bloat-o-meter i386-T41-laptop.1/vmlinux i386-T41-laptop.2/vmlinux 
add/remove: 0/0 grow/shrink: 9/7 up/down: 78/-107 (-29)
function                                     old     new   delta
__get_user_pages                             717     751     +34
st_read                                     1936    1944      +8
shmem_truncate_range                        1660    1667      +7
pci_create_slot                              410     417      +7
sg_build_indirect                            449     455      +6
n_tty_read                                  1336    1342      +6
find_vma_prepare                             103     108      +5
as_update_iohist                             617     621      +4
ntfs_readdir                                3426    3427      +1
enlarge_buffer                               343     341      -2
__get_free_pages                              36      33      -3
dma_generic_alloc_coherent                   207     202      -5
mempool_alloc_pages                           33      17     -16
futex_lock_pi                               2120    2104     -16
kallsyms_lookup_name                         102      82     -20
cache_alloc_refill                          1171    1126     -45

I'm going to retry this with a NUMA config.  

-- Dave

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