linux-kernel - Re: [PATCH] [MIPS] Hibernation: only save pages in system ram

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Date:	Fri, 3 Jul 2009 00:22:05 +0100
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Wu Zhangjin <wuzhangjin@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mips@...ux-mips.org,
	Pavel Machek <pavel@....cz>, Wu Zhangjin <wuzj@...ote.com>
Subject: Re: [PATCH] [MIPS] Hibernation: only save pages in system ram

On Tue, Jun 30, 2009 at 10:52:50PM +0800, Wu Zhangjin wrote:

> From: Wu Zhangjin <wuzj@...ote.com>
> 
> when using hibernation(STD) with CONFIG_FLATMEM in linux-mips-64bit, it
> fails for the current mips-specific hibernation implementation save the
> pages in all of the memory space(except the nosave section) and make
> there will be not enough memory left to the STD task itself, and then
> fail. in reality, we only need to save the pages in system rams.
> 
> here is the reason why it fail:
> 
> kernel/power/snapshot.c:
> 
> static void mark_nosave_pages(struct memory_bitmap *bm)
> {
> 		...
> 		if (pfn_valid(pfn)) {
> 			...
> 		}
> }
> 
> arch/mips/include/asm/page.h:
> 
> 	...
> 	#ifdef CONFIG_FLATMEM
> 
> 	#define pfn_valid(pfn)		((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
> 
> 	#elif defined(CONFIG_SPARSEMEM)
> 
> 	/* pfn_valid is defined in linux/mmzone.h */
> 	...
> 
> we can rewrite pfn_valid(pfn) to fix this problem, but I really do not
> want to touch such a widely-used macro, so, I used another solution:
> 
> static struct page *saveable_page(struct zone *zone, unsigned long pfn)
> {
> 	...
> 	if ( .... pfn_is_nosave(pfn)
> 		return NULL;
> 	...
> }
> 
> and pfn_is_nosave is implemented in arch/mips/power/cpu.c, so, hacking
> this one is better.

No - pfn_valid() is broken, so it should be fixed.  Commit
752fbeb2e3555c0d236e992f1195fd7ce30e728d introduced the breakage.  It
seemed to assume that the valid range for PFNs doesn't start at 0 but
some higher number but got that entirely wrong..

#define ARCH_PFN_OFFSET         PFN_UP(PHYS_OFFSET)
#define pfn_valid(pfn)         ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)

works nicely when PHYS_OFFSET is 0 - as for most MIPS systems and goes
horribly wrong otherwise.  So I suggest below patch.

  Ralf

Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>

 arch/mips/include/asm/page.h |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/arch/mips/include/asm/page.h b/arch/mips/include/asm/page.h
index dc0eaa7..96a14a4 100644
--- a/arch/mips/include/asm/page.h
+++ b/arch/mips/include/asm/page.h
@@ -165,7 +165,14 @@ typedef struct { unsigned long pgprot; } pgprot_t;
 
 #ifdef CONFIG_FLATMEM
 
-#define pfn_valid(pfn)		((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr)
+#define pfn_valid(pfn)							\
+({									\
+	unsigned long __pfn = (pfn);					\
+	/* avoid <linux/bootmem.h> include hell */			\
+	extern unsigned long min_low_pfn;				\
+									\
+	__pfn >= min_low_pfn && __pfn < max_mapnr;			\
+})
 
 #elif defined(CONFIG_SPARSEMEM)
 
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