linux-kernel - Re: arch/x86/mm/ioremap unification grew by 10x

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Message-Id: <1203275382.27987.20.camel@localhost.localdomain>
Date:	Sun, 17 Feb 2008 19:09:42 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Linux Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	"Huang, Ying" <ying.huang@...el.com>, Ying <ying.huang@...el.com>
Subject: Re: arch/x86/mm/ioremap unification grew by 10x


On Fri, 2008-02-15 at 17:17 -0600, Matt Mackall wrote:
> On Fri, 2008-02-15 at 15:21 -0600, Matt Mackall wrote:
> > On Fri, 2008-02-15 at 21:32 +0100, Sam Ravnborg wrote:
> > > On Fri, Feb 15, 2008 at 02:25:54PM -0600, Matt Mackall wrote:
> > > > In 2.6.24 defconfig, my build stats show ioremap_32.o was 1.8k. In
> > > > 2.6.25-rc1, the unified ioremap.o is 20.8k.
> > > 
> > > Just an observation - 17 commits touches said file after
> > > the unification (at least in latest -linus).
> > 
> > Correction: those numbers should be halved. So we're going from .9k to
> > 10.4k.
> 
> And here's most of the cause:
> 
> 000002b8 00000124 T early_ioremap
> 00001000 00001000 t bm_pte
> 00002000 00000004 T early_ioremap_debug
> 
> static __initdata pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)]
> 				__attribute__((aligned(PAGE_SIZE)));
> 
> Double ouch. First, this isn't in BSS. Second, even though it's
> initdata, the alignment slop won't get recovered.

551889a6e2a24a9c06fd453ea03b57b7746ffdc0 (the reason you CC'd me) only
changed this from unsigned long[1024] to pte_t[PAGE_SIZE/sizeof(pte_t)]

-static __initdata unsigned long bm_pte[1024]
+static __initdata pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)]
                                __attribute__((aligned(PAGE_SIZE)));

I don't think that would have changed anything in this respect. It seems
to have been that way since 0947b2f31ca1ea1211d3cde2dbd8fcec579ef395
when it was added (Huang Ying CC'd).

> Don't we have a special section for page-aligned crap so it doesn't
> waste most of two pages?

We have .bss.page_aligned and it seems appropriate to use it.

Ian.

--- 
From ac954372c1ed7830148bdea1e4283856c05c354f Mon Sep 17 00:00:00 2001
From: Ian Campbell <ijc@...lion.org.uk>
Date: Sun, 17 Feb 2008 19:08:34 +0000
Subject: [PATCH] x86: bm_pte can be placed in .bss.page_aligned.

    text	   data	    bss	    dec	    hex	filename
    -   3388	   8236	      4	  11628	   2d6c	../build-32/arch/x86/mm/ioremap.o
    +   3388	     48	   4100	   7536	   1d70	../build-32/arch/x86/mm/ioremap.o

Signed-off-by: Ian Campbell <ijc@...lion.org.uk>
Cc: Matt Mackall <mpm@...enic.com>
Cc: Sam Ravnborg <sam@...nborg.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Huang Ying <ying.huang@...el.com>
---
 arch/x86/mm/ioremap.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
index 69f4981..c62ecbd 100644
--- a/arch/x86/mm/ioremap.c
+++ b/arch/x86/mm/ioremap.c
@@ -262,8 +262,8 @@ static int __init early_ioremap_debug_setup(char *str)
 early_param("early_ioremap_debug", early_ioremap_debug_setup);
 
 static __initdata int after_paging_init;
-static __initdata pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)]
-				__attribute__((aligned(PAGE_SIZE)));
+static pte_t bm_pte[PAGE_SIZE/sizeof(pte_t)]
+		__attribute__((__section__(".bss.page_aligned")));
 
 static inline pmd_t * __init early_ioremap_pmd(unsigned long addr)
 {
-- 
1.5.4


-- 
Ian Campbell

In which level of metalanguage are you now speaking?

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