[PATCH] Tight check of pfn_valid on sparsemem - v3

[PATCH] Tight check of pfn_valid on sparsemem - v3

[Minchan Kim]

Changelog since v2
 o Change some function names
 o Remove mark_memmap_hole in memmap bring up
 o Change CONFIG_SPARSEMEM with CONFIG_ARCH_HAS_HOLES_MEMORYMODEL 
 
I have a plan following as after this patch is acked.

TODO:
1) expand pfn_valid to FALTMEM in ARM
I think we can enhance pfn_valid of FLATMEM in ARM.
Now it is doing binary search and it's expesive.
First of all, After we merge this patch, I expand it to FALTMEM of ARM.

2) remove memmap_valid_within
We can remove memmap_valid_within by strict pfn_valid's tight check.

3) Optimize hole check in sparsemem
In case of spasemem, we can optimize pfn_valid through defining new flag
like SECTION_HAS_HOLE of hole mem_section. 

== CUT HERE ==

Kukjin reported oops happen while he change min_free_kbytes
http://www.spinics.net/lists/arm-kernel/msg92894.html
It happen by memory map on sparsemem.

The system has a memory map following as.
     section 0             section 1              section 2
0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000
SECTION_SIZE_BITS 28(256M)

It means section 0 is an incompletely filled section.
Nontheless, current pfn_valid of sparsemem checks pfn loosely.
It checks only mem_section's validation but ARM can free mem_map on hole
to save memory space. So in above case, pfn on 0x25000000 can pass pfn_valid's
validation check. It's not what we want.

We can match section size to smallest valid size.(ex, above case, 16M)
But Russell doesn't like it due to mem_section's memory overhead with different
configuration(ex, 512K section).

I tried to add valid pfn range in mem_section but everyone doesn't like it
due to size overhead. This patch is suggested by KAMEZAWA-san.
I just fixed compile error and change some naming.

This patch registers address of mem_section to memmap itself's page struct's
pg->private field. This means the page is used for memmap of the section.
Otherwise, the page is used for other purpose and memmap has a hole.

This patch is based on mmotm-2010-07-19

Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reported-by: Kukjin Kim <kgene.kim@samsung.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Russell King <linux@arm.linux.org.uk>
---
 arch/arm/mm/init.c                  |    4 +++-
 include/linux/mmzone.h              |   22 +++++++++++++++++++++-
 mm/mmzone.c                         |   34 ++++++++++++++++++++++++++++++++++
 5 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index f6a9994..25e2670 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -482,8 +482,10 @@ free_memmap(int node, unsigned long start_pfn, unsigned long end_pfn)
 	 * If there are free pages between these,
 	 * free the section of the memmap array.
 	 */
-	if (pg < pgend)
+	if (pg < pgend) {
+ 		mark_invalid_memmap(pg >> PAGE_SHIFT, pgend >> PAGE_SHIFT);
 		free_bootmem_node(NODE_DATA(node), pg, pgend - pg);
+	}
 }
 
 /*
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index b4d109e..a3195bd 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -15,6 +15,7 @@
 #include <linux/seqlock.h>
 #include <linux/nodemask.h>
 #include <linux/pageblock-flags.h>
+#include <linux/mm_types.h>
 #include <generated/bounds.h>
 #include <asm/atomic.h>
 #include <asm/page.h>
@@ -1049,11 +1050,30 @@ static inline struct mem_section *__pfn_to_section(unsigned long pfn)
 	return __nr_to_section(pfn_to_section_nr(pfn));
 }
 
+void mark_invalid_memmap(unsigned long start, unsigned long end);
+
+#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
+#define MEMMAP_HOLE	(0x1UL)
+static inline int memmap_valid(unsigned long pfn)
+{
+	struct page *page = pfn_to_page(pfn);
+	struct page *__pg = virt_to_page(page);
+	return !(__pg->private & MEMMAP_HOLE);
+}
+#else
+static inline int memmap_valid(unsigned long pfn)
+{
+	return 1;
+}
+#endif
+
 static inline int pfn_valid(unsigned long pfn)
 {
+	struct mem_section *ms;
 	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
 		return 0;
-	return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
+	ms = __nr_to_section(pfn_to_section_nr(pfn));
+	return valid_section(ms) && memmap_valid(pfn);
 }
 
 static inline int pfn_present(unsigned long pfn)
diff --git a/mm/mmzone.c b/mm/mmzone.c
index f5b7d17..7c84e5e 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -86,4 +86,38 @@ int memmap_valid_within(unsigned long pfn,
 
 	return 1;
 }
+
+/*
+ * Fill pg->private on hole memmap with MEMMAP_HOLE.
+ * pfn_valid() will check this later. (see include/linux/mmzone.h)
+ * Evenry arch should call
+ * 	mark_invalid_memmap(start, end) # for all holes in mem_map.
+ * please see usage in ARM.
+ */
+void mark_invalid_memmap(unsigned long start, unsigned long end)
+{
+	struct mem_section *ms;
+	unsigned long pos, next;
+	struct page *pg;
+	void *memmap, *mapend;
+
+	for (pos = start; pos < end; pos = next) {
+		next = (pos + PAGES_PER_SECTION) & PAGE_SECTION_MASK;
+		ms = __pfn_to_section(pos);
+		if (!valid_section(ms))
+			continue;
+
+		for (memmap = (void*)pfn_to_page(pos),
+			/* The last page in section */
+			mapend = pfn_to_page(next-1);
+			memmap < mapend; memmap += PAGE_SIZE) {
+			pg = virt_to_page(memmap);
+			pg->private = MEMMAP_HOLE;
+		}
+	}
+}
+#else
+void mark_invalid_memmap(unsigned long start, unsigned long end)
+{
+}
 #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
-- 
1.7.0.5

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Re: [PATCH] Tight check of pfn_valid on sparsemem - v3

[Balbir Singh]

On Sun, Jul 25, 2010 at 7:32 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
> Changelog since v2
>  o Change some function names
>  o Remove mark_memmap_hole in memmap bring up
>  o Change CONFIG_SPARSEMEM with CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
>
> I have a plan following as after this patch is acked.
>
> TODO:
> 1) expand pfn_valid to FALTMEM in ARM
> I think we can enhance pfn_valid of FLATMEM in ARM.
> Now it is doing binary search and it's expesive.
> First of all, After we merge this patch, I expand it to FALTMEM of ARM.
>
> 2) remove memmap_valid_within
> We can remove memmap_valid_within by strict pfn_valid's tight check.
>
> 3) Optimize hole check in sparsemem
> In case of spasemem, we can optimize pfn_valid through defining new flag
> like SECTION_HAS_HOLE of hole mem_section.
>

Is there an assumption somewhere that assumes that page->private will
always have MEMMAP_HOLE set when the pfn is invalid, independent of
the context in which it is invoked? BTW, I'd also recommend moving
over to using set_page_private() and page_private() wrappers (makes
the code easier to search)

Balbir

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RE: [PATCH] Tight check of pfn_valid on sparsemem - v3

[Penttilä Mika]

> Changelog since v2
>  o Change some function names
>  o Remove mark_memmap_hole in memmap bring up
>  o Change CONFIG_SPARSEMEM with CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
> 
> I have a plan following as after this patch is acked.
> 
> TODO:
> 1) expand pfn_valid to FALTMEM in ARM
> I think we can enhance pfn_valid of FLATMEM in ARM.
> Now it is doing binary search and it's expesive.
> First of all, After we merge this patch, I expand it to FALTMEM of ARM.
> 
> 2) remove memmap_valid_within
> We can remove memmap_valid_within by strict pfn_valid's tight check.
> 
> 3) Optimize hole check in sparsemem
> In case of spasemem, we can optimize pfn_valid through defining new
> flag
> like SECTION_HAS_HOLE of hole mem_section.
> 
> == CUT HERE ==
> 
> Kukjin reported oops happen while he change min_free_kbytes
> http://www.spinics.net/lists/arm-kernel/msg92894.html
> It happen by memory map on sparsemem.
> 
> The system has a memory map following as.
>      section 0             section 1              section 2
> 0x20000000-0x25000000, 0x40000000-0x50000000, 0x50000000-0x58000000
> SECTION_SIZE_BITS 28(256M)
> 
> It means section 0 is an incompletely filled section.
> Nontheless, current pfn_valid of sparsemem checks pfn loosely.
> It checks only mem_section's validation but ARM can free mem_map on
> hole
> to save memory space. So in above case, pfn on 0x25000000 can pass
> pfn_valid's
> validation check. It's not what we want.
> 
> We can match section size to smallest valid size.(ex, above case, 16M)
> But Russell doesn't like it due to mem_section's memory overhead with
> different
> configuration(ex, 512K section).
> 
> I tried to add valid pfn range in mem_section but everyone doesn't like
> it
> due to size overhead. This patch is suggested by KAMEZAWA-san.
> I just fixed compile error and change some naming.
> 
> This patch registers address of mem_section to memmap itself's page
> struct's
> pg->private field. This means the page is used for memmap of the
> section.
> Otherwise, the page is used for other purpose and memmap has a hole.
> 
> This patch is based on mmotm-2010-07-19
> 
> Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Reported-by: Kukjin Kim <kgene.kim@samsung.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Russell King <linux@arm.linux.org.uk>
> ---
>  arch/arm/mm/init.c                  |    4 +++-
>  include/linux/mmzone.h              |   22 +++++++++++++++++++++-
>  mm/mmzone.c                         |   34
> ++++++++++++++++++++++++++++++++++
>  5 files changed, 58 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index f6a9994..25e2670 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -482,8 +482,10 @@ free_memmap(int node, unsigned long start_pfn,
> unsigned long end_pfn)
>  	 * If there are free pages between these,
>  	 * free the section of the memmap array.
>  	 */
> -	if (pg < pgend)
> +	if (pg < pgend) {
> + 		mark_invalid_memmap(pg >> PAGE_SHIFT, pgend >> PAGE_SHIFT);
>  		free_bootmem_node(NODE_DATA(node), pg, pgend - pg);
> +	}
>  }
> 
>  /*
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index b4d109e..a3195bd 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -15,6 +15,7 @@
>  #include <linux/seqlock.h>
>  #include <linux/nodemask.h>
>  #include <linux/pageblock-flags.h>
> +#include <linux/mm_types.h>
>  #include <generated/bounds.h>
>  #include <asm/atomic.h>
>  #include <asm/page.h>
> @@ -1049,11 +1050,30 @@ static inline struct mem_section
> *__pfn_to_section(unsigned long pfn)
>  	return __nr_to_section(pfn_to_section_nr(pfn));
>  }
> 
> +void mark_invalid_memmap(unsigned long start, unsigned long end);
> +
> +#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
> +#define MEMMAP_HOLE	(0x1UL)
> +static inline int memmap_valid(unsigned long pfn)
> +{
> +	struct page *page = pfn_to_page(pfn);
> +	struct page *__pg = virt_to_page(page);
> +	return !(__pg->private & MEMMAP_HOLE);
> +}
> +#else
> +static inline int memmap_valid(unsigned long pfn)
> +{
> +	return 1;
> +}
> +#endif
> +
>  static inline int pfn_valid(unsigned long pfn)
>  {
> +	struct mem_section *ms;
>  	if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
>  		return 0;
> -	return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
> +	ms = __nr_to_section(pfn_to_section_nr(pfn));
> +	return valid_section(ms) && memmap_valid(pfn);
>  }
> 
>  static inline int pfn_present(unsigned long pfn)
> diff --git a/mm/mmzone.c b/mm/mmzone.c
> index f5b7d17..7c84e5e 100644
> --- a/mm/mmzone.c
> +++ b/mm/mmzone.c
> @@ -86,4 +86,38 @@ int memmap_valid_within(unsigned long pfn,
> 
>  	return 1;
>  }
> +
> +/*
> + * Fill pg->private on hole memmap with MEMMAP_HOLE.
> + * pfn_valid() will check this later. (see include/linux/mmzone.h)
> + * Evenry arch should call
> + * 	mark_invalid_memmap(start, end) # for all holes in mem_map.
> + * please see usage in ARM.
> + */
> +void mark_invalid_memmap(unsigned long start, unsigned long end)
> +{
> +	struct mem_section *ms;
> +	unsigned long pos, next;
> +	struct page *pg;
> +	void *memmap, *mapend;
> +
> +	for (pos = start; pos < end; pos = next) {
> +		next = (pos + PAGES_PER_SECTION) & PAGE_SECTION_MASK;
> +		ms = __pfn_to_section(pos);
> +		if (!valid_section(ms))
> +			continue;
> +
> +		for (memmap = (void*)pfn_to_page(pos),
> +			/* The last page in section */
> +			mapend = pfn_to_page(next-1);
> +			memmap < mapend; memmap += PAGE_SIZE) {
> +			pg = virt_to_page(memmap);
> +			pg->private = MEMMAP_HOLE;
> +		}
> +	}
> +}
> +#else
> +void mark_invalid_memmap(unsigned long start, unsigned long end)
> +{
> +}
>  #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
> --



I don't think this works because if the memmap pages get reused, the corresponding struct page->private could be used by chance in such a way that it has the value of MEMMAP_HOLE. Of course unlikely but possible. And after all the whole point of freeing part of the memmap is that it could be reused.

--Mika



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Re: [PATCH] Tight check of pfn_valid on sparsemem - v3

[Minchan Kim]

On Mon, Jul 26, 2010 at 2:03 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
> On Sun, Jul 25, 2010 at 7:32 PM, Minchan Kim <minchan.kim@gmail.com> wrote:
>> Changelog since v2
>>  o Change some function names
>>  o Remove mark_memmap_hole in memmap bring up
>>  o Change CONFIG_SPARSEMEM with CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
>>
>> I have a plan following as after this patch is acked.
>>
>> TODO:
>> 1) expand pfn_valid to FALTMEM in ARM
>> I think we can enhance pfn_valid of FLATMEM in ARM.
>> Now it is doing binary search and it's expesive.
>> First of all, After we merge this patch, I expand it to FALTMEM of ARM.
>>
>> 2) remove memmap_valid_within
>> We can remove memmap_valid_within by strict pfn_valid's tight check.
>>
>> 3) Optimize hole check in sparsemem
>> In case of spasemem, we can optimize pfn_valid through defining new flag
>> like SECTION_HAS_HOLE of hole mem_section.
>>
>
> Is there an assumption somewhere that assumes that page->private will
> always have MEMMAP_HOLE set when the pfn is invalid, independent of
> the context in which it is invoked? BTW, I'd also recommend moving

zzzzz.... I needed sleep.
Will fix and resend.

> over to using set_page_private() and page_private() wrappers (makes
> the code easier to search)

Okay.
Thanks for pointing me out, Balbir.

>
> Balbir
>



-- 
Kind regards,
Minchan Kim

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Re: [PATCH] Tight check of pfn_valid on sparsemem - v3

[Minchan Kim]

2010/7/26 Penttilä Mika <mika.penttila@ixonos.com>:
> I don't think this works because if the memmap pages get reused, the corresponding struct page->private could be used by chance in such a way that it has the value of MEMMAP_HOLE. Of course unlikely but possible. And after all the whole point of freeing part of the memmap is that it could be reused.
>

You're absolutely right.
Previous version, I didn't do such as.
In this version, I wanted to remove dependency of page->private and
mem_section to identify hole memmap for using it in FLATMEM of ARM but
make mistake.
I will resend the patch

Thanks for careful review.

> --Mika
>
>
>
>



-- 
Kind regards,
Minchan Kim

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