[PATCH] mm,x86: remove debug_pagealloc_enabled

[PATCH] mm,x86: remove debug_pagealloc_enabled

[Stanislaw Gruszka]

When (no)bootmem finish operation, it pass pages to buddy allocator.
Since debug_pagealloc_enabled is not set, we will do not protect pages,
what is not what we want with CONFIG_DEBUG_PAGEALLOC=y.

To fix remove debug_pagealloc_enabled. That variable was introduced by
commit 12d6f21e "x86: do not PSE on CONFIG_DEBUG_PAGEALLOC=y" to get
more CPA (change page attribude) code testing. But currently we have
CONFIG_CPA_DEBUG, which test CPA.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
---
 arch/x86/mm/pageattr.c |    6 ------
 include/linux/mm.h     |   10 ----------
 init/main.c            |    5 -----
 mm/debug-pagealloc.c   |    3 ---
 4 files changed, 0 insertions(+), 24 deletions(-)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index f9e5267..5031eef 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -1334,12 +1334,6 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
 	}
 
 	/*
-	 * If page allocator is not up yet then do not call c_p_a():
-	 */
-	if (!debug_pagealloc_enabled)
-		return;
-
-	/*
 	 * The return value is ignored as the calls cannot fail.
 	 * Large pages for identity mappings are not used at boot time
 	 * and hence no memory allocations during large page split.
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 3dc3a8c..0a22db1 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1537,23 +1537,13 @@ static inline void vm_stat_account(struct mm_struct *mm,
 #endif /* CONFIG_PROC_FS */
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
-extern int debug_pagealloc_enabled;
-
 extern void kernel_map_pages(struct page *page, int numpages, int enable);
-
-static inline void enable_debug_pagealloc(void)
-{
-	debug_pagealloc_enabled = 1;
-}
 #ifdef CONFIG_HIBERNATION
 extern bool kernel_page_present(struct page *page);
 #endif /* CONFIG_HIBERNATION */
 #else
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable) {}
-static inline void enable_debug_pagealloc(void)
-{
-}
 #ifdef CONFIG_HIBERNATION
 static inline bool kernel_page_present(struct page *page) { return true; }
 #endif /* CONFIG_HIBERNATION */
diff --git a/init/main.c b/init/main.c
index 217ed23..99c4ba3 100644
--- a/init/main.c
+++ b/init/main.c
@@ -282,10 +282,6 @@ static int __init unknown_bootoption(char *param, char *val)
 	return 0;
 }
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-int __read_mostly debug_pagealloc_enabled = 0;
-#endif
-
 static int __init init_setup(char *str)
 {
 	unsigned int i;
@@ -597,7 +593,6 @@ asmlinkage void __init start_kernel(void)
 	}
 #endif
 	page_cgroup_init();
-	enable_debug_pagealloc();
 	debug_objects_mem_init();
 	kmemleak_init();
 	setup_per_cpu_pageset();
diff --git a/mm/debug-pagealloc.c b/mm/debug-pagealloc.c
index 7cea557..789ff70 100644
--- a/mm/debug-pagealloc.c
+++ b/mm/debug-pagealloc.c
@@ -95,9 +95,6 @@ static void unpoison_pages(struct page *page, int n)
 
 void kernel_map_pages(struct page *page, int numpages, int enable)
 {
-	if (!debug_pagealloc_enabled)
-		return;
-
 	if (enable)
 		unpoison_pages(page, numpages);
 	else
-- 
1.7.1

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Re: [PATCH] mm,x86: remove debug_pagealloc_enabled

[Stanislaw Gruszka]

On Wed, Nov 16, 2011 at 04:43:52PM +0100, Stanislaw Gruszka wrote:
> When (no)bootmem finish operation, it pass pages to buddy allocator.
> Since debug_pagealloc_enabled is not set, we will do not protect pages,
> what is not what we want with CONFIG_DEBUG_PAGEALLOC=y.
> 
> To fix remove debug_pagealloc_enabled. That variable was introduced by
> commit 12d6f21e "x86: do not PSE on CONFIG_DEBUG_PAGEALLOC=y" to get
> more CPA (change page attribude) code testing. But currently we have
> CONFIG_CPA_DEBUG, which test CPA.

Note this is more like fix than cleanup. Without patch, pages are not
protected until they are allocated and then freed again, what may
not happen if system is not used intensively.

If that patch can not be accepted, I think we should just go through
all free pages and mark then as not-presen in enable_debug_pagealloc()

Stanislaw

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Re: [PATCH] mm,x86: remove debug_pagealloc_enabled

[Mel Gorman]

On Wed, Nov 16, 2011 at 04:43:52PM +0100, Stanislaw Gruszka wrote:
> When (no)bootmem finish operation, it pass pages to buddy allocator.
> Since debug_pagealloc_enabled is not set, we will do not protect pages,
> what is not what we want with CONFIG_DEBUG_PAGEALLOC=y.
> 
> To fix remove debug_pagealloc_enabled. That variable was introduced by
> commit 12d6f21e "x86: do not PSE on CONFIG_DEBUG_PAGEALLOC=y" to get
> more CPA (change page attribude) code testing. But currently we have
> CONFIG_CPA_DEBUG, which test CPA.
> 
> Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>

If no one objects to the impact on CPA testing, I see no problem with
this. I would assume that many bugs related to CPA would be rattled out
by now

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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