linux-kernel - Re: [PATCH] kernel parameter vmalloc size fix

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Date:	Thu, 26 Jun 2008 14:14:30 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave Young <hidave.darkstar@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, hpa@...or.com,
	the arch/x86 maintainers <x86@...nel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [PATCH] kernel parameter vmalloc size fix


* Dave Young <hidave.darkstar@...il.com> wrote:

> I do some test about this last weekend, there's some questions, could 
> you help to fix it?
> 
> 1. MAXMEM :
>  (-__PAGE_OFFSET - __VMALLOC_RESERVE).
> The space after VMALLOC_END is included as well, seting it to
> (VMALLOC_END - PAGE_OFFSET - __VMALLOC_RESERVE), is it right?
> 
> 2. VMALLOC_OFFSET is not considered in __VMALLOC_RESERVE
> Should fixed by adding VMALLOC_OFFSET to it.
> 
> 3. VMALLOC_START :
>  (((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) & ~(VMALLOC_OFFSET - 1))
> So it's not always 8M, bigger than 8M possible.
> Set it to ((unsigned long)high_memory + VMALLOC_OFFSET), is it right?
> 
> Attached the proposed patch. please give some advice.

i've ported it to tip/master, see the patch below. Yinghai, what do you 
think about this change?

	Ingo

---
 arch/x86/mm/pgtable_32.c     |    3 ++-
 include/asm-x86/page_32.h    |    1 -
 include/asm-x86/pgtable_32.h |    5 +++--
 3 files changed, 5 insertions(+), 4 deletions(-)

Index: tip/arch/x86/mm/pgtable_32.c
===================================================================
--- tip.orig/arch/x86/mm/pgtable_32.c
+++ tip/arch/x86/mm/pgtable_32.c
@@ -171,7 +171,8 @@ static int __init parse_vmalloc(char *ar
 	if (!arg)
 		return -EINVAL;
 
-	__VMALLOC_RESERVE = memparse(arg, &arg);
+	/* Add VMALLOC_OFFSET to the parsed value due to vm area guard hole*/
+	__VMALLOC_RESERVE = memparse(arg, &arg) + VMALLOC_OFFSET;
 	return 0;
 }
 early_param("vmalloc", parse_vmalloc);
Index: tip/include/asm-x86/page_32.h
===================================================================
--- tip.orig/include/asm-x86/page_32.h
+++ tip/include/asm-x86/page_32.h
@@ -95,7 +95,6 @@ extern unsigned int __VMALLOC_RESERVE;
 extern int sysctl_legacy_va_layout;
 
 #define VMALLOC_RESERVE		((unsigned long)__VMALLOC_RESERVE)
-#define MAXMEM			(-__PAGE_OFFSET - __VMALLOC_RESERVE)
 
 extern void find_low_pfn_range(void);
 extern unsigned long init_memory_mapping(unsigned long start,
Index: tip/include/asm-x86/pgtable_32.h
===================================================================
--- tip.orig/include/asm-x86/pgtable_32.h
+++ tip/include/asm-x86/pgtable_32.h
@@ -56,8 +56,7 @@ void paging_init(void);
  * area for the same reason. ;)
  */
 #define VMALLOC_OFFSET	(8 * 1024 * 1024)
-#define VMALLOC_START	(((unsigned long)high_memory + 2 * VMALLOC_OFFSET - 1) \
-			 & ~(VMALLOC_OFFSET - 1))
+#define VMALLOC_START	((unsigned long)high_memory + VMALLOC_OFFSET)
 #ifdef CONFIG_X86_PAE
 #define LAST_PKMAP 512
 #else
@@ -73,6 +72,8 @@ void paging_init(void);
 # define VMALLOC_END	(FIXADDR_START - 2 * PAGE_SIZE)
 #endif
 
+#define MAXMEM	(VMALLOC_END - PAGE_OFFSET - __VMALLOC_RESERVE)
+
 /*
  * Define this if things work differently on an i386 and an i486:
  * it will (on an i486) warn about kernel memory accesses that are

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