[PATCH v3 0/3] Optimize CONFIG_DEBUG_PAGEALLOC

[PATCH v3 0/3] Optimize CONFIG_DEBUG_PAGEALLOC

[Christian Borntraeger]

Andrew, since the arch patches depend on the base patch, maybe the mm
tree is the right one? I have acks/reviews for the s390/x86 part.


As CONFIG_DEBUG_PAGEALLOC can be enabled/disabled via kernel
parameters we can optimize some cases by checking the enablement
state.

I have done s390 and x86 as examples.
s390 should be ok, I tested several combinations, x86 seems to
work as well.

Power can probably do the same, Michael/Ben?
I am not sure about sparc. Sparc seems to allocate the TSB buffer
really early. David?


V2->V3:
- Fix whitespace/indent breakage in s390 patch
V1->V2:
- replace DEBUG_PAGEALLOC(disabled/enabled) with DEBUG_PAGEALLOC
  dump_stack for s390/x86
- add /* CONFIG_DEBUG_PAGEALLOC */ to else and endif


Christian Borntraeger (3):
  mm: provide debug_pagealloc_enabled() without CONFIG_DEBUG_PAGEALLOC
  x86: query dynamic DEBUG_PAGEALLOC setting
  s390: query dynamic DEBUG_PAGEALLOC setting

 arch/s390/kernel/dumpstack.c |  6 +++---
 arch/s390/mm/vmem.c          | 10 ++++------
 arch/x86/kernel/dumpstack.c  |  5 ++---
 arch/x86/mm/init.c           |  7 ++++---
 arch/x86/mm/pageattr.c       | 14 ++++----------
 include/linux/mm.h           |  9 +++++++--
 6 files changed, 24 insertions(+), 27 deletions(-)

-- 
2.3.0

[PATCH v3 0/3] Optimize CONFIG_DEBUG_PAGEALLOC

[Christian Borntraeger]

Andrew, since the arch patches depend on the base patch, maybe the mm
tree is the right one? I have acks/reviews for the s390/x86 part.


As CONFIG_DEBUG_PAGEALLOC can be enabled/disabled via kernel
parameters we can optimize some cases by checking the enablement
state.

I have done s390 and x86 as examples.
s390 should be ok, I tested several combinations, x86 seems to
work as well.

Power can probably do the same, Michael/Ben?
I am not sure about sparc. Sparc seems to allocate the TSB buffer
really early. David?


V2->V3:
- Fix whitespace/indent breakage in s390 patch
V1->V2:
- replace DEBUG_PAGEALLOC(disabled/enabled) with DEBUG_PAGEALLOC
  dump_stack for s390/x86
- add /* CONFIG_DEBUG_PAGEALLOC */ to else and endif


Christian Borntraeger (3):
  mm: provide debug_pagealloc_enabled() without CONFIG_DEBUG_PAGEALLOC
  x86: query dynamic DEBUG_PAGEALLOC setting
  s390: query dynamic DEBUG_PAGEALLOC setting

 arch/s390/kernel/dumpstack.c |  6 +++---
 arch/s390/mm/vmem.c          | 10 ++++------
 arch/x86/kernel/dumpstack.c  |  5 ++---
 arch/x86/mm/init.c           |  7 ++++---
 arch/x86/mm/pageattr.c       | 14 ++++----------
 include/linux/mm.h           |  9 +++++++--
 6 files changed, 24 insertions(+), 27 deletions(-)

-- 
2.3.0

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[PATCH v3 1/3] mm: provide debug_pagealloc_enabled() without CONFIG_DEBUG_PAGEALLOC

[Christian Borntraeger]

We can provide debug_pagealloc_enabled() also if CONFIG_DEBUG_PAGEALLOC
is not set. It will return false in that case.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/mm.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1cd22f..ae84716 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2194,13 +2194,18 @@ kernel_map_pages(struct page *page, int numpages, int enable)
 #ifdef CONFIG_HIBERNATION
 extern bool kernel_page_present(struct page *page);
 #endif /* CONFIG_HIBERNATION */
-#else
+#else  /* CONFIG_DEBUG_PAGEALLOC */
+static inline bool debug_pagealloc_enabled(void)
+{
+	return false;
+}
+
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable) {}
 #ifdef CONFIG_HIBERNATION
 static inline bool kernel_page_present(struct page *page) { return true; }
 #endif /* CONFIG_HIBERNATION */
-#endif
+#endif /* CONFIG_DEBUG_PAGEALLOC */
 
 #ifdef __HAVE_ARCH_GATE_AREA
 extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm);
-- 
2.3.0

[PATCH v3 1/3] mm: provide debug_pagealloc_enabled() without CONFIG_DEBUG_PAGEALLOC

[Christian Borntraeger]

We can provide debug_pagealloc_enabled() also if CONFIG_DEBUG_PAGEALLOC
is not set. It will return false in that case.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/mm.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f1cd22f..ae84716 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2194,13 +2194,18 @@ kernel_map_pages(struct page *page, int numpages, int enable)
 #ifdef CONFIG_HIBERNATION
 extern bool kernel_page_present(struct page *page);
 #endif /* CONFIG_HIBERNATION */
-#else
+#else  /* CONFIG_DEBUG_PAGEALLOC */
+static inline bool debug_pagealloc_enabled(void)
+{
+	return false;
+}
+
 static inline void
 kernel_map_pages(struct page *page, int numpages, int enable) {}
 #ifdef CONFIG_HIBERNATION
 static inline bool kernel_page_present(struct page *page) { return true; }
 #endif /* CONFIG_HIBERNATION */
-#endif
+#endif /* CONFIG_DEBUG_PAGEALLOC */
 
 #ifdef __HAVE_ARCH_GATE_AREA
 extern struct vm_area_struct *get_gate_vma(struct mm_struct *mm);
-- 
2.3.0

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[PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

We can use debug_pagealloc_enabled() to check if we can map
the identity mapping with 2MB pages. We can also add the state
into the dump_stack output.

The patch does not touch the code for the 1GB pages, which ignored
CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/dumpstack.c |  5 ++---
 arch/x86/mm/init.c          |  7 ++++---
 arch/x86/mm/pageattr.c      | 14 ++++----------
 3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 9c30acf..32e5699 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
 #ifdef CONFIG_SMP
 	printk("SMP ");
 #endif
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	printk("DEBUG_PAGEALLOC ");
-#endif
+	if (debug_pagealloc_enabled())
+		printk("DEBUG_PAGEALLOC ");
 #ifdef CONFIG_KASAN
 	printk("KASAN");
 #endif
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 493f541..39823fd 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -150,13 +150,14 @@ static int page_size_mask;
 
 static void __init probe_page_size_mask(void)
 {
-#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
+#if !defined(CONFIG_KMEMCHECK)
 	/*
-	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
+	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
+	 * use small pages.
 	 * This will simplify cpa(), which otherwise needs to support splitting
 	 * large pages into small in interrupt context, etc.
 	 */
-	if (cpu_has_pse)
+	if (cpu_has_pse && !debug_pagealloc_enabled())
 		page_size_mask |= 1 << PG_LEVEL_2M;
 #endif
 
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index fc6a4c8..5f68987 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -106,12 +106,6 @@ static inline unsigned long highmap_end_pfn(void)
 
 #endif
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-# define debug_pagealloc 1
-#else
-# define debug_pagealloc 0
-#endif
-
 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
@@ -708,10 +702,10 @@ static int split_large_page(struct cpa_data *cpa, pte_t *kpte,
 {
 	struct page *base;
 
-	if (!debug_pagealloc)
+	if (!debug_pagealloc_enabled())
 		spin_unlock(&cpa_lock);
 	base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
-	if (!debug_pagealloc)
+	if (!debug_pagealloc_enabled())
 		spin_lock(&cpa_lock);
 	if (!base)
 		return -ENOMEM;
@@ -1331,10 +1325,10 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
 		if (cpa->flags & (CPA_ARRAY | CPA_PAGES_ARRAY))
 			cpa->numpages = 1;
 
-		if (!debug_pagealloc)
+		if (!debug_pagealloc_enabled())
 			spin_lock(&cpa_lock);
 		ret = __change_page_attr(cpa, checkalias);
-		if (!debug_pagealloc)
+		if (!debug_pagealloc_enabled())
 			spin_unlock(&cpa_lock);
 		if (ret)
 			return ret;
-- 
2.3.0

[PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

We can use debug_pagealloc_enabled() to check if we can map
the identity mapping with 2MB pages. We can also add the state
into the dump_stack output.

The patch does not touch the code for the 1GB pages, which ignored
CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/dumpstack.c |  5 ++---
 arch/x86/mm/init.c          |  7 ++++---
 arch/x86/mm/pageattr.c      | 14 ++++----------
 3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 9c30acf..32e5699 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
 #ifdef CONFIG_SMP
 	printk("SMP ");
 #endif
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	printk("DEBUG_PAGEALLOC ");
-#endif
+	if (debug_pagealloc_enabled())
+		printk("DEBUG_PAGEALLOC ");
 #ifdef CONFIG_KASAN
 	printk("KASAN");
 #endif
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 493f541..39823fd 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -150,13 +150,14 @@ static int page_size_mask;
 
 static void __init probe_page_size_mask(void)
 {
-#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
+#if !defined(CONFIG_KMEMCHECK)
 	/*
-	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
+	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
+	 * use small pages.
 	 * This will simplify cpa(), which otherwise needs to support splitting
 	 * large pages into small in interrupt context, etc.
 	 */
-	if (cpu_has_pse)
+	if (cpu_has_pse && !debug_pagealloc_enabled())
 		page_size_mask |= 1 << PG_LEVEL_2M;
 #endif
 
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index fc6a4c8..5f68987 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -106,12 +106,6 @@ static inline unsigned long highmap_end_pfn(void)
 
 #endif
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
-# define debug_pagealloc 1
-#else
-# define debug_pagealloc 0
-#endif
-
 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
@@ -708,10 +702,10 @@ static int split_large_page(struct cpa_data *cpa, pte_t *kpte,
 {
 	struct page *base;
 
-	if (!debug_pagealloc)
+	if (!debug_pagealloc_enabled())
 		spin_unlock(&cpa_lock);
 	base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0);
-	if (!debug_pagealloc)
+	if (!debug_pagealloc_enabled())
 		spin_lock(&cpa_lock);
 	if (!base)
 		return -ENOMEM;
@@ -1331,10 +1325,10 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias)
 		if (cpa->flags & (CPA_ARRAY | CPA_PAGES_ARRAY))
 			cpa->numpages = 1;
 
-		if (!debug_pagealloc)
+		if (!debug_pagealloc_enabled())
 			spin_lock(&cpa_lock);
 		ret = __change_page_attr(cpa, checkalias);
-		if (!debug_pagealloc)
+		if (!debug_pagealloc_enabled())
 			spin_unlock(&cpa_lock);
 		if (ret)
 			return ret;
-- 
2.3.0

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[PATCH v3 3/3] s390: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

We can use debug_pagealloc_enabled() to check if we can map
the identity mapping with 1MB/2GB pages as well as to print
the current setting in dump_stack.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 arch/s390/kernel/dumpstack.c |  6 +++---
 arch/s390/mm/vmem.c          | 10 ++++------
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/s390/kernel/dumpstack.c b/arch/s390/kernel/dumpstack.c
index dc8e204..e57eb22 100644
--- a/arch/s390/kernel/dumpstack.c
+++ b/arch/s390/kernel/dumpstack.c
@@ -11,6 +11,7 @@
 #include <linux/export.h>
 #include <linux/kdebug.h>
 #include <linux/ptrace.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <asm/processor.h>
@@ -185,9 +186,8 @@ void die(struct pt_regs *regs, const char *str)
 #ifdef CONFIG_SMP
 	printk("SMP ");
 #endif
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	printk("DEBUG_PAGEALLOC");
-#endif
+	if (debug_pagealloc_enabled())
+		printk("DEBUG_PAGEALLOC");
 	printk("\n");
 	notify_die(DIE_OOPS, str, regs, 0, regs->int_code & 0xffff, SIGSEGV);
 	print_modules();
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index ef7d6c8..d27fccba 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -94,16 +94,15 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 			pgd_populate(&init_mm, pg_dir, pu_dir);
 		}
 		pu_dir = pud_offset(pg_dir, address);
-#ifndef CONFIG_DEBUG_PAGEALLOC
 		if (MACHINE_HAS_EDAT2 && pud_none(*pu_dir) && address &&
-		    !(address & ~PUD_MASK) && (address + PUD_SIZE <= end)) {
+		    !(address & ~PUD_MASK) && (address + PUD_SIZE <= end) &&
+		     !debug_pagealloc_enabled()) {
 			pud_val(*pu_dir) = __pa(address) |
 				_REGION_ENTRY_TYPE_R3 | _REGION3_ENTRY_LARGE |
 				(ro ? _REGION_ENTRY_PROTECT : 0);
 			address += PUD_SIZE;
 			continue;
 		}
-#endif
 		if (pud_none(*pu_dir)) {
 			pm_dir = vmem_pmd_alloc();
 			if (!pm_dir)
@@ -111,9 +110,9 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 			pud_populate(&init_mm, pu_dir, pm_dir);
 		}
 		pm_dir = pmd_offset(pu_dir, address);
-#ifndef CONFIG_DEBUG_PAGEALLOC
 		if (MACHINE_HAS_EDAT1 && pmd_none(*pm_dir) && address &&
-		    !(address & ~PMD_MASK) && (address + PMD_SIZE <= end)) {
+		    !(address & ~PMD_MASK) && (address + PMD_SIZE <= end) &&
+		    !debug_pagealloc_enabled()) {
 			pmd_val(*pm_dir) = __pa(address) |
 				_SEGMENT_ENTRY | _SEGMENT_ENTRY_LARGE |
 				_SEGMENT_ENTRY_YOUNG |
@@ -121,7 +120,6 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 			address += PMD_SIZE;
 			continue;
 		}
-#endif
 		if (pmd_none(*pm_dir)) {
 			pt_dir = vmem_pte_alloc(address);
 			if (!pt_dir)
-- 
2.3.0

[PATCH v3 3/3] s390: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

We can use debug_pagealloc_enabled() to check if we can map
the identity mapping with 1MB/2GB pages as well as to print
the current setting in dump_stack.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 arch/s390/kernel/dumpstack.c |  6 +++---
 arch/s390/mm/vmem.c          | 10 ++++------
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/s390/kernel/dumpstack.c b/arch/s390/kernel/dumpstack.c
index dc8e204..e57eb22 100644
--- a/arch/s390/kernel/dumpstack.c
+++ b/arch/s390/kernel/dumpstack.c
@@ -11,6 +11,7 @@
 #include <linux/export.h>
 #include <linux/kdebug.h>
 #include <linux/ptrace.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <asm/processor.h>
@@ -185,9 +186,8 @@ void die(struct pt_regs *regs, const char *str)
 #ifdef CONFIG_SMP
 	printk("SMP ");
 #endif
-#ifdef CONFIG_DEBUG_PAGEALLOC
-	printk("DEBUG_PAGEALLOC");
-#endif
+	if (debug_pagealloc_enabled())
+		printk("DEBUG_PAGEALLOC");
 	printk("\n");
 	notify_die(DIE_OOPS, str, regs, 0, regs->int_code & 0xffff, SIGSEGV);
 	print_modules();
diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
index ef7d6c8..d27fccba 100644
--- a/arch/s390/mm/vmem.c
+++ b/arch/s390/mm/vmem.c
@@ -94,16 +94,15 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 			pgd_populate(&init_mm, pg_dir, pu_dir);
 		}
 		pu_dir = pud_offset(pg_dir, address);
-#ifndef CONFIG_DEBUG_PAGEALLOC
 		if (MACHINE_HAS_EDAT2 && pud_none(*pu_dir) && address &&
-		    !(address & ~PUD_MASK) && (address + PUD_SIZE <= end)) {
+		    !(address & ~PUD_MASK) && (address + PUD_SIZE <= end) &&
+		     !debug_pagealloc_enabled()) {
 			pud_val(*pu_dir) = __pa(address) |
 				_REGION_ENTRY_TYPE_R3 | _REGION3_ENTRY_LARGE |
 				(ro ? _REGION_ENTRY_PROTECT : 0);
 			address += PUD_SIZE;
 			continue;
 		}
-#endif
 		if (pud_none(*pu_dir)) {
 			pm_dir = vmem_pmd_alloc();
 			if (!pm_dir)
@@ -111,9 +110,9 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 			pud_populate(&init_mm, pu_dir, pm_dir);
 		}
 		pm_dir = pmd_offset(pu_dir, address);
-#ifndef CONFIG_DEBUG_PAGEALLOC
 		if (MACHINE_HAS_EDAT1 && pmd_none(*pm_dir) && address &&
-		    !(address & ~PMD_MASK) && (address + PMD_SIZE <= end)) {
+		    !(address & ~PMD_MASK) && (address + PMD_SIZE <= end) &&
+		    !debug_pagealloc_enabled()) {
 			pmd_val(*pm_dir) = __pa(address) |
 				_SEGMENT_ENTRY | _SEGMENT_ENTRY_LARGE |
 				_SEGMENT_ENTRY_YOUNG |
@@ -121,7 +120,6 @@ static int vmem_add_mem(unsigned long start, unsigned long size, int ro)
 			address += PMD_SIZE;
 			continue;
 		}
-#endif
 		if (pmd_none(*pm_dir)) {
 			pt_dir = vmem_pte_alloc(address);
 			if (!pt_dir)
-- 
2.3.0

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Wed, 27 Jan 2016, Christian Borntraeger wrote:

> We can use debug_pagealloc_enabled() to check if we can map
> the identity mapping with 2MB pages. We can also add the state
> into the dump_stack output.
> 
> The patch does not touch the code for the 1GB pages, which ignored
> CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/kernel/dumpstack.c |  5 ++---
>  arch/x86/mm/init.c          |  7 ++++---
>  arch/x86/mm/pageattr.c      | 14 ++++----------
>  3 files changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 9c30acf..32e5699 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
>  #ifdef CONFIG_SMP
>  	printk("SMP ");
>  #endif
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	printk("DEBUG_PAGEALLOC ");
> -#endif
> +	if (debug_pagealloc_enabled())
> +		printk("DEBUG_PAGEALLOC ");
>  #ifdef CONFIG_KASAN
>  	printk("KASAN");
>  #endif
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 493f541..39823fd 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -150,13 +150,14 @@ static int page_size_mask;
>  
>  static void __init probe_page_size_mask(void)
>  {
> -#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
> +#if !defined(CONFIG_KMEMCHECK)
>  	/*
> -	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
> +	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
> +	 * use small pages.
>  	 * This will simplify cpa(), which otherwise needs to support splitting
>  	 * large pages into small in interrupt context, etc.
>  	 */
> -	if (cpu_has_pse)
> +	if (cpu_has_pse && !debug_pagealloc_enabled())
>  		page_size_mask |= 1 << PG_LEVEL_2M;
>  #endif
>  

I would have thought free_init_pages() would be modified to use 
debug_pagealloc_enabled() as well?

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Wed, 27 Jan 2016, Christian Borntraeger wrote:

> We can use debug_pagealloc_enabled() to check if we can map
> the identity mapping with 2MB pages. We can also add the state
> into the dump_stack output.
> 
> The patch does not touch the code for the 1GB pages, which ignored
> CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/kernel/dumpstack.c |  5 ++---
>  arch/x86/mm/init.c          |  7 ++++---
>  arch/x86/mm/pageattr.c      | 14 ++++----------
>  3 files changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 9c30acf..32e5699 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
>  #ifdef CONFIG_SMP
>  	printk("SMP ");
>  #endif
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	printk("DEBUG_PAGEALLOC ");
> -#endif
> +	if (debug_pagealloc_enabled())
> +		printk("DEBUG_PAGEALLOC ");
>  #ifdef CONFIG_KASAN
>  	printk("KASAN");
>  #endif
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 493f541..39823fd 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -150,13 +150,14 @@ static int page_size_mask;
>  
>  static void __init probe_page_size_mask(void)
>  {
> -#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
> +#if !defined(CONFIG_KMEMCHECK)
>  	/*
> -	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
> +	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
> +	 * use small pages.
>  	 * This will simplify cpa(), which otherwise needs to support splitting
>  	 * large pages into small in interrupt context, etc.
>  	 */
> -	if (cpu_has_pse)
> +	if (cpu_has_pse && !debug_pagealloc_enabled())
>  		page_size_mask |= 1 << PG_LEVEL_2M;
>  #endif
>  

I would have thought free_init_pages() would be modified to use 
debug_pagealloc_enabled() as well?

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[David Rientjes via Linuxppc-dev]

[-- Attachment #1: Type: message/rfc822, Size: 5626 bytes --]

From: David Rientjes <rientjes@google.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net, Joonsoo Kim <iamjoonsoo.kim@lge.com>, davej@codemonkey.org.uk
Subject: Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting
Date: Wed, 27 Jan 2016 14:17:05 -0800 (PST)
Message-ID: <alpine.DEB.2.10.1601271414180.23510@chino.kir.corp.google.com>

On Wed, 27 Jan 2016, Christian Borntraeger wrote:

> We can use debug_pagealloc_enabled() to check if we can map
> the identity mapping with 2MB pages. We can also add the state
> into the dump_stack output.
> 
> The patch does not touch the code for the 1GB pages, which ignored
> CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/kernel/dumpstack.c |  5 ++---
>  arch/x86/mm/init.c          |  7 ++++---
>  arch/x86/mm/pageattr.c      | 14 ++++----------
>  3 files changed, 10 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
> index 9c30acf..32e5699 100644
> --- a/arch/x86/kernel/dumpstack.c
> +++ b/arch/x86/kernel/dumpstack.c
> @@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
>  #ifdef CONFIG_SMP
>  	printk("SMP ");
>  #endif
> -#ifdef CONFIG_DEBUG_PAGEALLOC
> -	printk("DEBUG_PAGEALLOC ");
> -#endif
> +	if (debug_pagealloc_enabled())
> +		printk("DEBUG_PAGEALLOC ");
>  #ifdef CONFIG_KASAN
>  	printk("KASAN");
>  #endif
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 493f541..39823fd 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -150,13 +150,14 @@ static int page_size_mask;
>  
>  static void __init probe_page_size_mask(void)
>  {
> -#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
> +#if !defined(CONFIG_KMEMCHECK)
>  	/*
> -	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
> +	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
> +	 * use small pages.
>  	 * This will simplify cpa(), which otherwise needs to support splitting
>  	 * large pages into small in interrupt context, etc.
>  	 */
> -	if (cpu_has_pse)
> +	if (cpu_has_pse && !debug_pagealloc_enabled())
>  		page_size_mask |= 1 << PG_LEVEL_2M;
>  #endif
>  

I would have thought free_init_pages() would be modified to use 
debug_pagealloc_enabled() as well?

[-- Attachment #2: Type: text/plain, Size: 150 bytes --]

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Re: [PATCH v3 3/3] s390: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Wed, 27 Jan 2016, Christian Borntraeger wrote:

> We can use debug_pagealloc_enabled() to check if we can map
> the identity mapping with 1MB/2GB pages as well as to print
> the current setting in dump_stack.
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Acked-by: David Rientjes <rientjes@google.com>

Re: [PATCH v3 3/3] s390: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Wed, 27 Jan 2016, Christian Borntraeger wrote:

> We can use debug_pagealloc_enabled() to check if we can map
> the identity mapping with 1MB/2GB pages as well as to print
> the current setting in dump_stack.
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Acked-by: David Rientjes <rientjes@google.com>

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[David Rientjes via Linuxppc-dev]

[-- Attachment #1: Type: message/rfc822, Size: 3939 bytes --]

From: David Rientjes <rientjes@google.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net, Joonsoo Kim <iamjoonsoo.kim@lge.com>, davej@codemonkey.org.uk
Subject: Re: [PATCH v3 3/3] s390: query dynamic DEBUG_PAGEALLOC setting
Date: Wed, 27 Jan 2016 14:18:29 -0800 (PST)
Message-ID: <alpine.DEB.2.10.1601271418190.23510@chino.kir.corp.google.com>

On Wed, 27 Jan 2016, Christian Borntraeger wrote:

> We can use debug_pagealloc_enabled() to check if we can map
> the identity mapping with 1MB/2GB pages as well as to print
> the current setting in dump_stack.
> 
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>

Acked-by: David Rientjes <rientjes@google.com>

[-- Attachment #2: Type: text/plain, Size: 150 bytes --]

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

On 01/27/2016 11:17 PM, David Rientjes wrote:
> On Wed, 27 Jan 2016, Christian Borntraeger wrote:
> 
>> We can use debug_pagealloc_enabled() to check if we can map
>> the identity mapping with 2MB pages. We can also add the state
>> into the dump_stack output.
>>
>> The patch does not touch the code for the 1GB pages, which ignored
>> CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
>> ---
>>  arch/x86/kernel/dumpstack.c |  5 ++---
>>  arch/x86/mm/init.c          |  7 ++++---
>>  arch/x86/mm/pageattr.c      | 14 ++++----------
>>  3 files changed, 10 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
>> index 9c30acf..32e5699 100644
>> --- a/arch/x86/kernel/dumpstack.c
>> +++ b/arch/x86/kernel/dumpstack.c
>> @@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
>>  #ifdef CONFIG_SMP
>>  	printk("SMP ");
>>  #endif
>> -#ifdef CONFIG_DEBUG_PAGEALLOC
>> -	printk("DEBUG_PAGEALLOC ");
>> -#endif
>> +	if (debug_pagealloc_enabled())
>> +		printk("DEBUG_PAGEALLOC ");
>>  #ifdef CONFIG_KASAN
>>  	printk("KASAN");
>>  #endif
>> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>> index 493f541..39823fd 100644
>> --- a/arch/x86/mm/init.c
>> +++ b/arch/x86/mm/init.c
>> @@ -150,13 +150,14 @@ static int page_size_mask;
>>  
>>  static void __init probe_page_size_mask(void)
>>  {
>> -#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
>> +#if !defined(CONFIG_KMEMCHECK)
>>  	/*
>> -	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
>> +	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
>> +	 * use small pages.
>>  	 * This will simplify cpa(), which otherwise needs to support splitting
>>  	 * large pages into small in interrupt context, etc.
>>  	 */
>> -	if (cpu_has_pse)
>> +	if (cpu_has_pse && !debug_pagealloc_enabled())
>>  		page_size_mask |= 1 << PG_LEVEL_2M;
>>  #endif
>>  
> 
> I would have thought free_init_pages() would be modified to use 
> debug_pagealloc_enabled() as well?


Indeed, I only touched the identity mapping and dump stack.
The question is do we really want to change free_init_pages as well?
The unmapping during runtime causes significant overhead, but the
unmapping after init imposes almost no runtime overhead. Of course,
things get fishy now as what is enabled and what not.

Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
(in mm) now states
----snip----
By default this option will have a small overhead, e.g. by not
allowing the kernel mapping to be backed by large pages on some
architectures. Even bigger overhead comes when the debugging is
enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
command line parameter.
----snip----

So I am tempted to NOT change free_init_pages, but the x86 maintainers
can certainly decide differently. Ingo, Thomas, H. Peter, please advise.

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

On 01/27/2016 11:17 PM, David Rientjes wrote:
> On Wed, 27 Jan 2016, Christian Borntraeger wrote:
> 
>> We can use debug_pagealloc_enabled() to check if we can map
>> the identity mapping with 2MB pages. We can also add the state
>> into the dump_stack output.
>>
>> The patch does not touch the code for the 1GB pages, which ignored
>> CONFIG_DEBUG_PAGEALLOC. Do we need to fence this as well?
>>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
>> ---
>>  arch/x86/kernel/dumpstack.c |  5 ++---
>>  arch/x86/mm/init.c          |  7 ++++---
>>  arch/x86/mm/pageattr.c      | 14 ++++----------
>>  3 files changed, 10 insertions(+), 16 deletions(-)
>>
>> diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
>> index 9c30acf..32e5699 100644
>> --- a/arch/x86/kernel/dumpstack.c
>> +++ b/arch/x86/kernel/dumpstack.c
>> @@ -265,9 +265,8 @@ int __die(const char *str, struct pt_regs *regs, long err)
>>  #ifdef CONFIG_SMP
>>  	printk("SMP ");
>>  #endif
>> -#ifdef CONFIG_DEBUG_PAGEALLOC
>> -	printk("DEBUG_PAGEALLOC ");
>> -#endif
>> +	if (debug_pagealloc_enabled())
>> +		printk("DEBUG_PAGEALLOC ");
>>  #ifdef CONFIG_KASAN
>>  	printk("KASAN");
>>  #endif
>> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>> index 493f541..39823fd 100644
>> --- a/arch/x86/mm/init.c
>> +++ b/arch/x86/mm/init.c
>> @@ -150,13 +150,14 @@ static int page_size_mask;
>>  
>>  static void __init probe_page_size_mask(void)
>>  {
>> -#if !defined(CONFIG_DEBUG_PAGEALLOC) && !defined(CONFIG_KMEMCHECK)
>> +#if !defined(CONFIG_KMEMCHECK)
>>  	/*
>> -	 * For CONFIG_DEBUG_PAGEALLOC, identity mapping will use small pages.
>> +	 * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will
>> +	 * use small pages.
>>  	 * This will simplify cpa(), which otherwise needs to support splitting
>>  	 * large pages into small in interrupt context, etc.
>>  	 */
>> -	if (cpu_has_pse)
>> +	if (cpu_has_pse && !debug_pagealloc_enabled())
>>  		page_size_mask |= 1 << PG_LEVEL_2M;
>>  #endif
>>  
> 
> I would have thought free_init_pages() would be modified to use 
> debug_pagealloc_enabled() as well?


Indeed, I only touched the identity mapping and dump stack.
The question is do we really want to change free_init_pages as well?
The unmapping during runtime causes significant overhead, but the
unmapping after init imposes almost no runtime overhead. Of course,
things get fishy now as what is enabled and what not.

Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
(in mm) now states
----snip----
By default this option will have a small overhead, e.g. by not
allowing the kernel mapping to be backed by large pages on some
architectures. Even bigger overhead comes when the debugging is
enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
command line parameter.
----snip----

So I am tempted to NOT change free_init_pages, but the x86 maintainers
can certainly decide differently. Ingo, Thomas, H. Peter, please advise.


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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Thu, 28 Jan 2016, Christian Borntraeger wrote:

> Indeed, I only touched the identity mapping and dump stack.
> The question is do we really want to change free_init_pages as well?
> The unmapping during runtime causes significant overhead, but the
> unmapping after init imposes almost no runtime overhead. Of course,
> things get fishy now as what is enabled and what not.
> 
> Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
> (in mm) now states
> ----snip----
> By default this option will have a small overhead, e.g. by not
> allowing the kernel mapping to be backed by large pages on some
> architectures. Even bigger overhead comes when the debugging is
> enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
> command line parameter.
> ----snip----
> 
> So I am tempted to NOT change free_init_pages, but the x86 maintainers
> can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
> 

I'm sorry, but I thought the discussion of the previous version of the 
patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
controlled by being enabled on the commandline and checked with 
debug_pagealloc_enabled().

I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
to enable more stuff.  It should either be all enabled by the commandline 
(or config option) or split into a separate entity.  
CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
the current state is very confusing about what is being done and what 
isn't.

It also wouldn't hurt to enumerate what is enabled and what isn't enabled 
in the Kconfig entry.

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Thu, 28 Jan 2016, Christian Borntraeger wrote:

> Indeed, I only touched the identity mapping and dump stack.
> The question is do we really want to change free_init_pages as well?
> The unmapping during runtime causes significant overhead, but the
> unmapping after init imposes almost no runtime overhead. Of course,
> things get fishy now as what is enabled and what not.
> 
> Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
> (in mm) now states
> ----snip----
> By default this option will have a small overhead, e.g. by not
> allowing the kernel mapping to be backed by large pages on some
> architectures. Even bigger overhead comes when the debugging is
> enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
> command line parameter.
> ----snip----
> 
> So I am tempted to NOT change free_init_pages, but the x86 maintainers
> can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
> 

I'm sorry, but I thought the discussion of the previous version of the 
patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
controlled by being enabled on the commandline and checked with 
debug_pagealloc_enabled().

I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
to enable more stuff.  It should either be all enabled by the commandline 
(or config option) or split into a separate entity.  
CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
the current state is very confusing about what is being done and what 
isn't.

It also wouldn't hurt to enumerate what is enabled and what isn't enabled 
in the Kconfig entry.

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[David Rientjes via Linuxppc-dev]

[-- Attachment #1: Type: message/rfc822, Size: 5371 bytes --]

From: David Rientjes <rientjes@google.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net, Joonsoo Kim <iamjoonsoo.kim@lge.com>, davej@codemonkey.org.uk
Subject: Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting
Date: Thu, 28 Jan 2016 15:03:39 -0800 (PST)
Message-ID: <alpine.DEB.2.10.1601281500160.31035@chino.kir.corp.google.com>

On Thu, 28 Jan 2016, Christian Borntraeger wrote:

> Indeed, I only touched the identity mapping and dump stack.
> The question is do we really want to change free_init_pages as well?
> The unmapping during runtime causes significant overhead, but the
> unmapping after init imposes almost no runtime overhead. Of course,
> things get fishy now as what is enabled and what not.
> 
> Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
> (in mm) now states
> ----snip----
> By default this option will have a small overhead, e.g. by not
> allowing the kernel mapping to be backed by large pages on some
> architectures. Even bigger overhead comes when the debugging is
> enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
> command line parameter.
> ----snip----
> 
> So I am tempted to NOT change free_init_pages, but the x86 maintainers
> can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
> 

I'm sorry, but I thought the discussion of the previous version of the 
patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
controlled by being enabled on the commandline and checked with 
debug_pagealloc_enabled().

I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
to enable more stuff.  It should either be all enabled by the commandline 
(or config option) or split into a separate entity.  
CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
the current state is very confusing about what is being done and what 
isn't.

It also wouldn't hurt to enumerate what is enabled and what isn't enabled 
in the Kconfig entry.

[-- Attachment #2: Type: text/plain, Size: 150 bytes --]

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Thu, 28 Jan 2016, David Rientjes wrote:

> On Thu, 28 Jan 2016, Christian Borntraeger wrote:
> 
> > Indeed, I only touched the identity mapping and dump stack.
> > The question is do we really want to change free_init_pages as well?
> > The unmapping during runtime causes significant overhead, but the
> > unmapping after init imposes almost no runtime overhead. Of course,
> > things get fishy now as what is enabled and what not.
> > 
> > Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
> > (in mm) now states
> > ----snip----
> > By default this option will have a small overhead, e.g. by not
> > allowing the kernel mapping to be backed by large pages on some
> > architectures. Even bigger overhead comes when the debugging is
> > enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
> > command line parameter.
> > ----snip----
> > 
> > So I am tempted to NOT change free_init_pages, but the x86 maintainers
> > can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
> > 
> 
> I'm sorry, but I thought the discussion of the previous version of the 
> patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
> controlled by being enabled on the commandline and checked with 
> debug_pagealloc_enabled().
> 
> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> to enable more stuff.  It should either be all enabled by the commandline 
> (or config option) or split into a separate entity.  
> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> the current state is very confusing about what is being done and what 
> isn't.
> 

Ping?

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[David Rientjes]

On Thu, 28 Jan 2016, David Rientjes wrote:

> On Thu, 28 Jan 2016, Christian Borntraeger wrote:
> 
> > Indeed, I only touched the identity mapping and dump stack.
> > The question is do we really want to change free_init_pages as well?
> > The unmapping during runtime causes significant overhead, but the
> > unmapping after init imposes almost no runtime overhead. Of course,
> > things get fishy now as what is enabled and what not.
> > 
> > Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
> > (in mm) now states
> > ----snip----
> > By default this option will have a small overhead, e.g. by not
> > allowing the kernel mapping to be backed by large pages on some
> > architectures. Even bigger overhead comes when the debugging is
> > enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
> > command line parameter.
> > ----snip----
> > 
> > So I am tempted to NOT change free_init_pages, but the x86 maintainers
> > can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
> > 
> 
> I'm sorry, but I thought the discussion of the previous version of the 
> patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
> controlled by being enabled on the commandline and checked with 
> debug_pagealloc_enabled().
> 
> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> to enable more stuff.  It should either be all enabled by the commandline 
> (or config option) or split into a separate entity.  
> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> the current state is very confusing about what is being done and what 
> isn't.
> 

Ping?

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[David Rientjes via Linuxppc-dev]

[-- Attachment #1: Type: message/rfc822, Size: 5486 bytes --]

From: David Rientjes <rientjes@google.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, davem@davemloft.net, Joonsoo Kim <iamjoonsoo.kim@lge.com>, davej@codemonkey.org.uk
Subject: Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting
Date: Tue, 2 Feb 2016 13:51:34 -0800 (PST)
Message-ID: <alpine.DEB.2.10.1602021351290.4977@chino.kir.corp.google.com>

On Thu, 28 Jan 2016, David Rientjes wrote:

> On Thu, 28 Jan 2016, Christian Borntraeger wrote:
> 
> > Indeed, I only touched the identity mapping and dump stack.
> > The question is do we really want to change free_init_pages as well?
> > The unmapping during runtime causes significant overhead, but the
> > unmapping after init imposes almost no runtime overhead. Of course,
> > things get fishy now as what is enabled and what not.
> > 
> > Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
> > (in mm) now states
> > ----snip----
> > By default this option will have a small overhead, e.g. by not
> > allowing the kernel mapping to be backed by large pages on some
> > architectures. Even bigger overhead comes when the debugging is
> > enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
> > command line parameter.
> > ----snip----
> > 
> > So I am tempted to NOT change free_init_pages, but the x86 maintainers
> > can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
> > 
> 
> I'm sorry, but I thought the discussion of the previous version of the 
> patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
> controlled by being enabled on the commandline and checked with 
> debug_pagealloc_enabled().
> 
> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> to enable more stuff.  It should either be all enabled by the commandline 
> (or config option) or split into a separate entity.  
> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> the current state is very confusing about what is being done and what 
> isn't.
> 

Ping?

[-- Attachment #2: Type: text/plain, Size: 150 bytes --]

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

On 02/02/2016 10:51 PM, David Rientjes wrote:
> On Thu, 28 Jan 2016, David Rientjes wrote:
> 
>> On Thu, 28 Jan 2016, Christian Borntraeger wrote:
>>
>>> Indeed, I only touched the identity mapping and dump stack.
>>> The question is do we really want to change free_init_pages as well?
>>> The unmapping during runtime causes significant overhead, but the
>>> unmapping after init imposes almost no runtime overhead. Of course,
>>> things get fishy now as what is enabled and what not.
>>>
>>> Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
>>> (in mm) now states
>>> ----snip----
>>> By default this option will have a small overhead, e.g. by not
>>> allowing the kernel mapping to be backed by large pages on some
>>> architectures. Even bigger overhead comes when the debugging is
>>> enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
>>> command line parameter.
>>> ----snip----
>>>
>>> So I am tempted to NOT change free_init_pages, but the x86 maintainers
>>> can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
>>>
>>
>> I'm sorry, but I thought the discussion of the previous version of the 
>> patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
>> controlled by being enabled on the commandline and checked with 
>> debug_pagealloc_enabled().
>>
>> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
>> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
>> to enable more stuff.  It should either be all enabled by the commandline 
>> (or config option) or split into a separate entity.  
>> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
>> the current state is very confusing about what is being done and what 
>> isn't.
>>
> 
> Ping?
> 
https://lkml.org/lkml/2016/1/29/266 
?

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

On 02/02/2016 10:51 PM, David Rientjes wrote:
> On Thu, 28 Jan 2016, David Rientjes wrote:
> 
>> On Thu, 28 Jan 2016, Christian Borntraeger wrote:
>>
>>> Indeed, I only touched the identity mapping and dump stack.
>>> The question is do we really want to change free_init_pages as well?
>>> The unmapping during runtime causes significant overhead, but the
>>> unmapping after init imposes almost no runtime overhead. Of course,
>>> things get fishy now as what is enabled and what not.
>>>
>>> Kconfig after my patch "mm/debug_pagealloc: Ask users for default setting of debug_pagealloc"
>>> (in mm) now states
>>> ----snip----
>>> By default this option will have a small overhead, e.g. by not
>>> allowing the kernel mapping to be backed by large pages on some
>>> architectures. Even bigger overhead comes when the debugging is
>>> enabled by DEBUG_PAGEALLOC_ENABLE_DEFAULT or the debug_pagealloc
>>> command line parameter.
>>> ----snip----
>>>
>>> So I am tempted to NOT change free_init_pages, but the x86 maintainers
>>> can certainly decide differently. Ingo, Thomas, H. Peter, please advise.
>>>
>>
>> I'm sorry, but I thought the discussion of the previous version of the 
>> patchset led to deciding that all CONFIG_DEBUG_PAGEALLOC behavior would be 
>> controlled by being enabled on the commandline and checked with 
>> debug_pagealloc_enabled().
>>
>> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
>> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
>> to enable more stuff.  It should either be all enabled by the commandline 
>> (or config option) or split into a separate entity.  
>> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
>> the current state is very confusing about what is being done and what 
>> isn't.
>>
> 
> Ping?
> 
https://lkml.org/lkml/2016/1/29/266 
?

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Andrew Morton]

On Tue, 2 Feb 2016 22:53:36 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> >> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> >> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> >> to enable more stuff.  It should either be all enabled by the commandline 
> >> (or config option) or split into a separate entity.  
> >> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> >> the current state is very confusing about what is being done and what 
> >> isn't.
> >>
> > 
> > Ping?
> > 
> https://lkml.org/lkml/2016/1/29/266 

That's already in linux-next so I can't apply it.

Well, I can, but it's a hassle.  What's happening here?

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Andrew Morton]

On Tue, 2 Feb 2016 22:53:36 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> >> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> >> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> >> to enable more stuff.  It should either be all enabled by the commandline 
> >> (or config option) or split into a separate entity.  
> >> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> >> the current state is very confusing about what is being done and what 
> >> isn't.
> >>
> > 
> > Ping?
> > 
> https://lkml.org/lkml/2016/1/29/266 

That's already in linux-next so I can't apply it.

Well, I can, but it's a hassle.  What's happening here?

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

On 02/02/2016 11:21 PM, Andrew Morton wrote:
> On Tue, 2 Feb 2016 22:53:36 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
>>>> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
>>>> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
>>>> to enable more stuff.  It should either be all enabled by the commandline 
>>>> (or config option) or split into a separate entity.  
>>>> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
>>>> the current state is very confusing about what is being done and what 
>>>> isn't.
>>>>
>>>
>>> Ping?
>>>
>> https://lkml.org/lkml/2016/1/29/266 
> 
> That's already in linux-next so I can't apply it.
> 
> Well, I can, but it's a hassle.  What's happening here?

I pushed it on my tree for kbuild testing purposes some days ago. 
Will drop so that it can go via mm.

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Christian Borntraeger]

On 02/02/2016 11:21 PM, Andrew Morton wrote:
> On Tue, 2 Feb 2016 22:53:36 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
>>>> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
>>>> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
>>>> to enable more stuff.  It should either be all enabled by the commandline 
>>>> (or config option) or split into a separate entity.  
>>>> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
>>>> the current state is very confusing about what is being done and what 
>>>> isn't.
>>>>
>>>
>>> Ping?
>>>
>> https://lkml.org/lkml/2016/1/29/266 
> 
> That's already in linux-next so I can't apply it.
> 
> Well, I can, but it's a hassle.  What's happening here?

I pushed it on my tree for kbuild testing purposes some days ago. 
Will drop so that it can go via mm.


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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Andrew Morton]

On Tue, 2 Feb 2016 23:37:50 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 02/02/2016 11:21 PM, Andrew Morton wrote:
> > On Tue, 2 Feb 2016 22:53:36 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> > 
> >>>> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> >>>> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> >>>> to enable more stuff.  It should either be all enabled by the commandline 
> >>>> (or config option) or split into a separate entity.  
> >>>> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> >>>> the current state is very confusing about what is being done and what 
> >>>> isn't.
> >>>>
> >>>
> >>> Ping?
> >>>
> >> https://lkml.org/lkml/2016/1/29/266 
> > 
> > That's already in linux-next so I can't apply it.
> > 
> > Well, I can, but it's a hassle.  What's happening here?
> 
> I pushed it on my tree for kbuild testing purposes some days ago. 
> Will drop so that it can go via mm.

There are other patches that I haven't merged because they were already
in -next.  In fact I think I dropped them because they later popped up
in -next.

Some or all of:

lib-spinlock_debugc-prevent-an-infinite-recursive-cycle-in-spin_dump.patch
mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
x86-query-dynamic-debug_pagealloc-setting.patch
s390-query-dynamic-debug_pagealloc-setting.patch
mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
x86-query-dynamic-debug_pagealloc-setting.patch
s390-query-dynamic-debug_pagealloc-setting.patch

So please resend everything which you think is needed.

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Andrew Morton]

On Tue, 2 Feb 2016 23:37:50 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 02/02/2016 11:21 PM, Andrew Morton wrote:
> > On Tue, 2 Feb 2016 22:53:36 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> > 
> >>>> I don't think we should have a CONFIG_DEBUG_PAGEALLOC that does some stuff 
> >>>> and then a commandline parameter or CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT 
> >>>> to enable more stuff.  It should either be all enabled by the commandline 
> >>>> (or config option) or split into a separate entity.  
> >>>> CONFIG_DEBUG_PAGEALLOC_LIGHT and CONFIG_DEBUG_PAGEALLOC would be fine, but 
> >>>> the current state is very confusing about what is being done and what 
> >>>> isn't.
> >>>>
> >>>
> >>> Ping?
> >>>
> >> https://lkml.org/lkml/2016/1/29/266 
> > 
> > That's already in linux-next so I can't apply it.
> > 
> > Well, I can, but it's a hassle.  What's happening here?
> 
> I pushed it on my tree for kbuild testing purposes some days ago. 
> Will drop so that it can go via mm.

There are other patches that I haven't merged because they were already
in -next.  In fact I think I dropped them because they later popped up
in -next.

Some or all of:

lib-spinlock_debugc-prevent-an-infinite-recursive-cycle-in-spin_dump.patch
mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
x86-query-dynamic-debug_pagealloc-setting.patch
s390-query-dynamic-debug_pagealloc-setting.patch
mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
x86-query-dynamic-debug_pagealloc-setting.patch
s390-query-dynamic-debug_pagealloc-setting.patch

So please resend everything which you think is needed.

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Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Stephen Rothwell]

Hi Andrew,

On Tue, 2 Feb 2016 15:04:35 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Tue, 2 Feb 2016 23:37:50 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
> > 
> > I pushed it on my tree for kbuild testing purposes some days ago. 
> > Will drop so that it can go via mm.  
> 
> There are other patches that I haven't merged because they were already
> in -next.  In fact I think I dropped them because they later popped up
> in -next.
> 
> Some or all of:
> 
> lib-spinlock_debugc-prevent-an-infinite-recursive-cycle-in-spin_dump.patch
> mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
> x86-query-dynamic-debug_pagealloc-setting.patch
> s390-query-dynamic-debug_pagealloc-setting.patch
> mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
> x86-query-dynamic-debug_pagealloc-setting.patch
> s390-query-dynamic-debug_pagealloc-setting.patch
> 
> So please resend everything which you think is needed.

Christian's tree will be empty in today's linux-next (I just refetched it).

-- 
Cheers,
Stephen Rothwell

Re: [PATCH v3 2/3] x86: query dynamic DEBUG_PAGEALLOC setting

[Stephen Rothwell]

Hi Andrew,

On Tue, 2 Feb 2016 15:04:35 -0800 Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Tue, 2 Feb 2016 23:37:50 +0100 Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> 
> > 
> > I pushed it on my tree for kbuild testing purposes some days ago. 
> > Will drop so that it can go via mm.  
> 
> There are other patches that I haven't merged because they were already
> in -next.  In fact I think I dropped them because they later popped up
> in -next.
> 
> Some or all of:
> 
> lib-spinlock_debugc-prevent-an-infinite-recursive-cycle-in-spin_dump.patch
> mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
> x86-query-dynamic-debug_pagealloc-setting.patch
> s390-query-dynamic-debug_pagealloc-setting.patch
> mm-provide-debug_pagealloc_enabled-without-config_debug_pagealloc.patch
> x86-query-dynamic-debug_pagealloc-setting.patch
> s390-query-dynamic-debug_pagealloc-setting.patch
> 
> So please resend everything which you think is needed.

Christian's tree will be empty in today's linux-next (I just refetched it).

-- 
Cheers,
Stephen Rothwell

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