linux-kernel - Re: [PATCH 2/3] x86/mm: Simplify for-loop in free_init

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Message-ID: <1342305489.8377.47.camel@joe2Laptop>
Date:	Sat, 14 Jul 2012 15:38:09 -0700
From:	Joe Perches <joe@...ches.com>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	Yinghai Lu <yinghai@...nel.org>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 2/3] x86/mm: Simplify for-loop in free_init_pages()

On Sat, 2012-07-14 at 23:48 +0300, Pekka Enberg wrote:
> On Sat, Jul 14, 2012 at 11:43 PM, Joe Perches <joe@...ches.com> wrote:
> > On Sat, 2012-07-14 at 13:36 -0700, Yinghai Lu wrote:
> >> On Sat, Jul 14, 2012 at 6:41 AM, Pekka Enberg <penberg@...nel.org> wrote:
> >> > As a cleanup, move initial "addr" assignment to the for-loop construct
> >> > in free_init_pages().
> >
> > Not really a good idea.
> 
> Of course it's a good idea. The current code flow makes no sense.
> 
> >> > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> > []
> >> > @@ -349,8 +349,6 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
> >> >         if (begin >= end)
> >> >                 return;
> >> >
> >> > -       addr = begin;
> >> > -
> >> >         /*
> >> >          * If debugging page accesses then do not free this memory but
> >> >          * mark them not present - any buggy init-section access will
> >> > @@ -371,7 +369,7 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
> >> >
> >> >         printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
> >> >
> >> > -       for (; addr < end; addr += PAGE_SIZE) {
> >> > +       for (addr = begin; addr < end; addr += PAGE_SIZE) {
> >> >                 ClearPageReserved(virt_to_page(addr));
> >> >                 init_page_count(virt_to_page(addr));
> >> >                 memset((void *)addr, POISON_FREE_INITMEM, PAGE_SIZE);
> >> > --
> >
> > Now there's an unused variable warning when CONFIG_DEBUG_PAGEALLOC
> 
> Sure, that needs fixing. It'd probably be simplest to introduce a
> __free_init_pages() helper.
> 

Perhaps:

 arch/x86/mm/init.c |   14 ++++++--------
 1 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index bc4e9d8..1023484 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -330,7 +330,6 @@ int devmem_is_allowed(unsigned long pagenr)
 
 void free_init_pages(char *what, unsigned long begin, unsigned long end)
 {
-	unsigned long addr;
 	unsigned long begin_aligned, end_aligned;
 
 	/* Make sure boundaries are page aligned */
@@ -345,8 +344,6 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
 	if (begin >= end)
 		return;
 
-	addr = begin;
-
 	/*
 	 * If debugging page accesses then do not free this memory but
 	 * mark them not present - any buggy init-section access will
@@ -367,12 +364,13 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
 
 	printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
 
-	for (; addr < end; addr += PAGE_SIZE) {
-		ClearPageReserved(virt_to_page(addr));
-		init_page_count(virt_to_page(addr));
-		memset((void *)addr, POISON_FREE_INITMEM, PAGE_SIZE);
-		free_page(addr);
+	while (begin < end) {
+		ClearPageReserved(virt_to_page(begin));
+		init_page_count(virt_to_page(begin));
+		memset((void *)begin, POISON_FREE_INITMEM, PAGE_SIZE);
+		free_page(begin);
 		totalram_pages++;
+		begin += PAGE_SIZE;
 	}
 #endif
 }


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