[PATCH 0/3] try to save some memory for kmem_cache in some cases

[PATCH 0/3] try to save some memory for kmem_cache in some cases

[Wei Yang]

kmem_cache is a frequently used data in kernel. During the code reading, I
found maybe we could save some space in some cases.

1. On 64bit arch, type int will occupy a word if it doesn't sit well.
2. cpu_slab->partial is just used when CONFIG_SLUB_CPU_PARTIAL is set
3. cpu_partial is just used when CONFIG_SLUB_CPU_PARTIAL is set, while just
save some space on 32bit arch.

Wei Yang (3):
  mm/slub: pack red_left_pad with another int to save a word
  mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL
  mm/slub: wrap kmem_cache->cpu_partial in config
    CONFIG_SLUB_CPU_PARTIAL

 include/linux/slub_def.h |  6 +++-
 mm/slub.c                | 88 ++++++++++++++++++++++++++++++++----------------
 2 files changed, 64 insertions(+), 30 deletions(-)

-- 
2.11.0

[PATCH 1/3] mm/slub: pack red_left_pad with another int to save a word

[Wei Yang]

On 64bit arch, struct is 8-bytes aligned, so int will occupy a word if it
doesn't sits well.

This patch pack red_left_pad with reserved to save 8 bytes for struct
kmem_cache on a 64bit arch.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 include/linux/slub_def.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 07ef550c6627..ec13aab32647 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -79,9 +79,9 @@ struct kmem_cache {
 	int inuse;		/* Offset to metadata */
 	int align;		/* Alignment */
 	int reserved;		/* Reserved bytes at the end of slabs */
+	int red_left_pad;	/* Left redzone padding size */
 	const char *name;	/* Name (only for display!) */
 	struct list_head list;	/* List of slab caches */
-	int red_left_pad;	/* Left redzone padding size */
 #ifdef CONFIG_SYSFS
 	struct kobject kobj;	/* For sysfs */
 #endif
-- 
2.11.0

[PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL

[Wei Yang]

cpu_slab's field partial is used when CONFIG_SLUB_CPU_PARTIAL is set, which
means we can save a pointer's space on each cpu for every slub item.

This patch wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL and wrap its
sysfs too.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 include/linux/slub_def.h |  2 ++
 mm/slub.c                | 16 +++++++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index ec13aab32647..0debd8df1a7d 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -41,7 +41,9 @@ struct kmem_cache_cpu {
 	void **freelist;	/* Pointer to next available object */
 	unsigned long tid;	/* Globally unique transaction id */
 	struct page *page;	/* The slab from which we are allocating */
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 	struct page *partial;	/* Partially allocated frozen slabs */
+#endif
 #ifdef CONFIG_SLUB_STATS
 	unsigned stat[NR_SLUB_STAT_ITEMS];
 #endif
diff --git a/mm/slub.c b/mm/slub.c
index 7f4bc7027ed5..fde499b6dad8 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2302,7 +2302,11 @@ static bool has_cpu_slab(int cpu, void *info)
 	struct kmem_cache *s = info;
 	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
 
-	return c->page || c->partial;
+	return c->page
+#ifdef CONFIG_SLUB_CPU_PARTIAL
+		|| c->partial
+#endif
+		;
 }
 
 static void flush_all(struct kmem_cache *s)
@@ -2511,7 +2515,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	page = c->page;
 	if (!page)
 		goto new_slab;
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 redo:
+#endif
 
 	if (unlikely(!node_match(page, node))) {
 		int searchnode = node;
@@ -2568,6 +2574,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 
 new_slab:
 
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 	if (c->partial) {
 		page = c->page = c->partial;
 		c->partial = page->next;
@@ -2575,6 +2582,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		c->freelist = NULL;
 		goto redo;
 	}
+#endif
 
 	freelist = new_slab_objects(s, gfpflags, node, &c);
 
@@ -4760,6 +4768,7 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
 			total += x;
 			nodes[node] += x;
 
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 			page = READ_ONCE(c->partial);
 			if (page) {
 				node = page_to_nid(page);
@@ -4772,6 +4781,7 @@ static ssize_t show_slab_objects(struct kmem_cache *s,
 				total += x;
 				nodes[node] += x;
 			}
+#endif
 		}
 	}
 
@@ -4980,6 +4990,7 @@ static ssize_t objects_partial_show(struct kmem_cache *s, char *buf)
 }
 SLAB_ATTR_RO(objects_partial);
 
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
 {
 	int objects = 0;
@@ -5010,6 +5021,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
 	return len + sprintf(buf + len, "\n");
 }
 SLAB_ATTR_RO(slabs_cpu_partial);
+#endif
 
 static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
 {
@@ -5364,7 +5376,9 @@ static struct attribute *slab_attrs[] = {
 	&destroy_by_rcu_attr.attr,
 	&shrink_attr.attr,
 	&reserved_attr.attr,
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 	&slabs_cpu_partial_attr.attr,
+#endif
 #ifdef CONFIG_SLUB_DEBUG
 	&total_objects_attr.attr,
 	&slabs_attr.attr,
-- 
2.11.0

Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL

[Matthew Wilcox]

On Sun, Apr 30, 2017 at 07:31:51PM +0800, Wei Yang wrote:
> @@ -2302,7 +2302,11 @@ static bool has_cpu_slab(int cpu, void *info)
>  	struct kmem_cache *s = info;
>  	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
>  
> -	return c->page || c->partial;
> +	return c->page
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
> +		|| c->partial
> +#endif
> +		;
>  }

No.  No way.  This is disgusting.

The right way to do this is to create an accessor like this:

#ifdef CONFIG_SLUB_CPU_PARTIAL
#define slub_cpu_partial(c)	((c)->partial)
#else
#define slub_cpu_partial(c)	0
#endif

And then the above becomes:

-	return c->page || c->partial;
+	return c->page || slub_cpu_partial(c);

All the other ifdefs go away, apart from these two:

> @@ -4980,6 +4990,7 @@ static ssize_t objects_partial_show(struct kmem_cache *s, char *buf)
>  }
>  SLAB_ATTR_RO(objects_partial);
>  
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>  {
>  	int objects = 0;
> @@ -5010,6 +5021,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>  	return len + sprintf(buf + len, "\n");
>  }
>  SLAB_ATTR_RO(slabs_cpu_partial);
> +#endif
>  
>  static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
>  {
> @@ -5364,7 +5376,9 @@ static struct attribute *slab_attrs[] = {
>  	&destroy_by_rcu_attr.attr,
>  	&shrink_attr.attr,
>  	&reserved_attr.attr,
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>  	&slabs_cpu_partial_attr.attr,
> +#endif
>  #ifdef CONFIG_SLUB_DEBUG
>  	&total_objects_attr.attr,
>  	&slabs_attr.attr,

Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL

[Wei Yang]

[-- Attachment #1: Type: text/plain, Size: 2151 bytes --]

On Sun, Apr 30, 2017 at 07:41:03PM -0700, Matthew Wilcox wrote:
>On Sun, Apr 30, 2017 at 07:31:51PM +0800, Wei Yang wrote:
>> @@ -2302,7 +2302,11 @@ static bool has_cpu_slab(int cpu, void *info)
>>  	struct kmem_cache *s = info;
>>  	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
>>  
>> -	return c->page || c->partial;
>> +	return c->page
>> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>> +		|| c->partial
>> +#endif
>> +		;
>>  }
>
>No.  No way.  This is disgusting.
>

Thanks for your comment. I believe you are right.

>The right way to do this is to create an accessor like this:
>
>#ifdef CONFIG_SLUB_CPU_PARTIAL
>#define slub_cpu_partial(c)	((c)->partial)
>#else
>#define slub_cpu_partial(c)	0

Since partial is a pointer to a page, would this be more proper?

#define slub_cpu_partial(c)	NULL

>#endif
>
>And then the above becomes:
>
>-	return c->page || c->partial;
>+	return c->page || slub_cpu_partial(c);
>
>All the other ifdefs go away, apart from these two:

Looks most of the ifdefs could be replaced by this format, while not all of
them. For example, the sysfs entry.

I would form another version with your suggestion.

Welcome any other comments :-)

>
>> @@ -4980,6 +4990,7 @@ static ssize_t objects_partial_show(struct kmem_cache *s, char *buf)
>>  }
>>  SLAB_ATTR_RO(objects_partial);
>>  
>> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>>  static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>>  {
>>  	int objects = 0;
>> @@ -5010,6 +5021,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>>  	return len + sprintf(buf + len, "\n");
>>  }
>>  SLAB_ATTR_RO(slabs_cpu_partial);
>> +#endif
>>  
>>  static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
>>  {
>> @@ -5364,7 +5376,9 @@ static struct attribute *slab_attrs[] = {
>>  	&destroy_by_rcu_attr.attr,
>>  	&shrink_attr.attr,
>>  	&reserved_attr.attr,
>> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>>  	&slabs_cpu_partial_attr.attr,
>> +#endif
>>  #ifdef CONFIG_SLUB_DEBUG
>>  	&total_objects_attr.attr,
>>  	&slabs_attr.attr,

-- 
Wei Yang
Help you, Help me

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Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL

[Wei Yang]

[-- Attachment #1: Type: text/plain, Size: 2072 bytes --]

On Sun, Apr 30, 2017 at 07:41:03PM -0700, Matthew Wilcox wrote:
>On Sun, Apr 30, 2017 at 07:31:51PM +0800, Wei Yang wrote:
>> @@ -2302,7 +2302,11 @@ static bool has_cpu_slab(int cpu, void *info)
>>  	struct kmem_cache *s = info;
>>  	struct kmem_cache_cpu *c = per_cpu_ptr(s->cpu_slab, cpu);
>>  
>> -	return c->page || c->partial;
>> +	return c->page
>> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>> +		|| c->partial
>> +#endif
>> +		;
>>  }
>
>No.  No way.  This is disgusting.
>
>The right way to do this is to create an accessor like this:
>
>#ifdef CONFIG_SLUB_CPU_PARTIAL
>#define slub_cpu_partial(c)	((c)->partial)
>#else
>#define slub_cpu_partial(c)	0
>#endif
>
>And then the above becomes:
>
>-	return c->page || c->partial;
>+	return c->page || slub_cpu_partial(c);
>
>All the other ifdefs go away, apart from these two:
>

Matthew

I have tried to replace the code with slub_cpu_partial(), it works fine on
most of cases except two:

1. slub_cpu_partial(c) = page->next;
2. page = READ_ONCE(slub_cpu_partial(c));

The sysfs part works fine.

So if you agree, I would leave these two parts as v1.

>> @@ -4980,6 +4990,7 @@ static ssize_t objects_partial_show(struct kmem_cache *s, char *buf)
>>  }
>>  SLAB_ATTR_RO(objects_partial);
>>  
>> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>>  static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>>  {
>>  	int objects = 0;
>> @@ -5010,6 +5021,7 @@ static ssize_t slabs_cpu_partial_show(struct kmem_cache *s, char *buf)
>>  	return len + sprintf(buf + len, "\n");
>>  }
>>  SLAB_ATTR_RO(slabs_cpu_partial);
>> +#endif
>>  
>>  static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
>>  {
>> @@ -5364,7 +5376,9 @@ static struct attribute *slab_attrs[] = {
>>  	&destroy_by_rcu_attr.attr,
>>  	&shrink_attr.attr,
>>  	&reserved_attr.attr,
>> +#ifdef CONFIG_SLUB_CPU_PARTIAL
>>  	&slabs_cpu_partial_attr.attr,
>> +#endif
>>  #ifdef CONFIG_SLUB_DEBUG
>>  	&total_objects_attr.attr,
>>  	&slabs_attr.attr,

-- 
Wei Yang
Help you, Help me

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Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL

[Matthew Wilcox]

On Mon, May 01, 2017 at 04:20:05PM +0800, Wei Yang wrote:
> I have tried to replace the code with slub_cpu_partial(), it works fine on
> most of cases except two:
> 
> 1. slub_cpu_partial(c) = page->next;

New accessor: slub_set_cpu_partial(c, p)

> 2. page = READ_ONCE(slub_cpu_partial(c));

OK, that one I haven't seen an existing pattern for yet.
slub_cpu_partial_read_once(c)?

Re: [PATCH 2/3] mm/slub: wrap cpu_slab->partial in CONFIG_SLUB_CPU_PARTIAL

[Wei Yang]

[-- Attachment #1: Type: text/plain, Size: 542 bytes --]

On Mon, May 01, 2017 at 07:39:30AM -0700, Matthew Wilcox wrote:
>On Mon, May 01, 2017 at 04:20:05PM +0800, Wei Yang wrote:
>> I have tried to replace the code with slub_cpu_partial(), it works fine on
>> most of cases except two:
>> 
>> 1. slub_cpu_partial(c) = page->next;
>
>New accessor: slub_set_cpu_partial(c, p)
>
>> 2. page = READ_ONCE(slub_cpu_partial(c));
>
>OK, that one I haven't seen an existing pattern for yet.
>slub_cpu_partial_read_once(c)?

Thanks~ You are really a genius.

-- 
Wei Yang
Help you, Help me

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[PATCH 3/3] mm/slub: wrap kmem_cache->cpu_partial in config CONFIG_SLUB_CPU_PARTIAL

[Wei Yang]

kmem_cache->cpu_partial is just used when CONFIG_SLUB_CPU_PARTIAL is set,
so wrap it with config CONFIG_SLUB_CPU_PARTIAL will save some space
on 32bit arch.

This patch wrap kmem_cache->cpu_partial in config CONFIG_SLUB_CPU_PARTIAL
and wrap its sysfs too.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
---
 include/linux/slub_def.h |  2 ++
 mm/slub.c                | 72 +++++++++++++++++++++++++++++-------------------
 2 files changed, 46 insertions(+), 28 deletions(-)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 0debd8df1a7d..477ab99800ed 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -69,7 +69,9 @@ struct kmem_cache {
 	int size;		/* The size of an object including meta data */
 	int object_size;	/* The size of an object without meta data */
 	int offset;		/* Free pointer offset. */
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 	int cpu_partial;	/* Number of per cpu partial objects to keep around */
+#endif
 	struct kmem_cache_order_objects oo;
 
 	/* Allocation and freeing of slabs */
diff --git a/mm/slub.c b/mm/slub.c
index fde499b6dad8..94978f27882a 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1829,7 +1829,10 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 			stat(s, CPU_PARTIAL_NODE);
 		}
 		if (!kmem_cache_has_cpu_partial(s)
-			|| available > s->cpu_partial / 2)
+#ifdef CONFIG_SLUB_CPU_PARTIAL
+			|| available > s->cpu_partial / 2
+#endif
+			)
 			break;
 
 	}
@@ -3418,6 +3421,39 @@ static void set_min_partial(struct kmem_cache *s, unsigned long min)
 	s->min_partial = min;
 }
 
+static void set_cpu_partial(struct kmem_cache *s)
+{
+#ifdef CONFIG_SLUB_CPU_PARTIAL
+	/*
+	 * cpu_partial determined the maximum number of objects kept in the
+	 * per cpu partial lists of a processor.
+	 *
+	 * Per cpu partial lists mainly contain slabs that just have one
+	 * object freed. If they are used for allocation then they can be
+	 * filled up again with minimal effort. The slab will never hit the
+	 * per node partial lists and therefore no locking will be required.
+	 *
+	 * This setting also determines
+	 *
+	 * A) The number of objects from per cpu partial slabs dumped to the
+	 *    per node list when we reach the limit.
+	 * B) The number of objects in cpu partial slabs to extract from the
+	 *    per node list when we run out of per cpu objects. We only fetch
+	 *    50% to keep some capacity around for frees.
+	 */
+	if (!kmem_cache_has_cpu_partial(s))
+		s->cpu_partial = 0;
+	else if (s->size >= PAGE_SIZE)
+		s->cpu_partial = 2;
+	else if (s->size >= 1024)
+		s->cpu_partial = 6;
+	else if (s->size >= 256)
+		s->cpu_partial = 13;
+	else
+		s->cpu_partial = 30;
+#endif
+}
+
 /*
  * calculate_sizes() determines the order and the distribution of data within
  * a slab object.
@@ -3576,33 +3612,7 @@ static int kmem_cache_open(struct kmem_cache *s, unsigned long flags)
 	 */
 	set_min_partial(s, ilog2(s->size) / 2);
 
-	/*
-	 * cpu_partial determined the maximum number of objects kept in the
-	 * per cpu partial lists of a processor.
-	 *
-	 * Per cpu partial lists mainly contain slabs that just have one
-	 * object freed. If they are used for allocation then they can be
-	 * filled up again with minimal effort. The slab will never hit the
-	 * per node partial lists and therefore no locking will be required.
-	 *
-	 * This setting also determines
-	 *
-	 * A) The number of objects from per cpu partial slabs dumped to the
-	 *    per node list when we reach the limit.
-	 * B) The number of objects in cpu partial slabs to extract from the
-	 *    per node list when we run out of per cpu objects. We only fetch
-	 *    50% to keep some capacity around for frees.
-	 */
-	if (!kmem_cache_has_cpu_partial(s))
-		s->cpu_partial = 0;
-	else if (s->size >= PAGE_SIZE)
-		s->cpu_partial = 2;
-	else if (s->size >= 1024)
-		s->cpu_partial = 6;
-	else if (s->size >= 256)
-		s->cpu_partial = 13;
-	else
-		s->cpu_partial = 30;
+	set_cpu_partial(s);
 
 #ifdef CONFIG_NUMA
 	s->remote_node_defrag_ratio = 1000;
@@ -3989,7 +3999,9 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
 	 * Disable empty slabs caching. Used to avoid pinning offline
 	 * memory cgroups by kmem pages that can be freed.
 	 */
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 	s->cpu_partial = 0;
+#endif
 	s->min_partial = 0;
 
 	/*
@@ -4929,6 +4941,7 @@ static ssize_t min_partial_store(struct kmem_cache *s, const char *buf,
 }
 SLAB_ATTR(min_partial);
 
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 static ssize_t cpu_partial_show(struct kmem_cache *s, char *buf)
 {
 	return sprintf(buf, "%u\n", s->cpu_partial);
@@ -4951,6 +4964,7 @@ static ssize_t cpu_partial_store(struct kmem_cache *s, const char *buf,
 	return length;
 }
 SLAB_ATTR(cpu_partial);
+#endif
 
 static ssize_t ctor_show(struct kmem_cache *s, char *buf)
 {
@@ -5363,7 +5377,9 @@ static struct attribute *slab_attrs[] = {
 	&objs_per_slab_attr.attr,
 	&order_attr.attr,
 	&min_partial_attr.attr,
+#ifdef CONFIG_SLUB_CPU_PARTIAL
 	&cpu_partial_attr.attr,
+#endif
 	&objects_attr.attr,
 	&objects_partial_attr.attr,
 	&partial_attr.attr,
-- 
2.11.0

Re: [PATCH 3/3] mm/slub: wrap kmem_cache->cpu_partial in config CONFIG_SLUB_CPU_PARTIAL

[Wei Yang]

[-- Attachment #1: Type: text/plain, Size: 5871 bytes --]

On Sun, Apr 30, 2017 at 07:31:52PM +0800, Wei Yang wrote:
>kmem_cache->cpu_partial is just used when CONFIG_SLUB_CPU_PARTIAL is set,
>so wrap it with config CONFIG_SLUB_CPU_PARTIAL will save some space
>on 32bit arch.
>
>This patch wrap kmem_cache->cpu_partial in config CONFIG_SLUB_CPU_PARTIAL
>and wrap its sysfs too.
>
>Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>---
> include/linux/slub_def.h |  2 ++
> mm/slub.c                | 72 +++++++++++++++++++++++++++++-------------------
> 2 files changed, 46 insertions(+), 28 deletions(-)
>
>diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
>index 0debd8df1a7d..477ab99800ed 100644
>--- a/include/linux/slub_def.h
>+++ b/include/linux/slub_def.h
>@@ -69,7 +69,9 @@ struct kmem_cache {
> 	int size;		/* The size of an object including meta data */
> 	int object_size;	/* The size of an object without meta data */
> 	int offset;		/* Free pointer offset. */
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> 	int cpu_partial;	/* Number of per cpu partial objects to keep around */
>+#endif
> 	struct kmem_cache_order_objects oo;
> 
> 	/* Allocation and freeing of slabs */
>diff --git a/mm/slub.c b/mm/slub.c
>index fde499b6dad8..94978f27882a 100644
>--- a/mm/slub.c
>+++ b/mm/slub.c
>@@ -1829,7 +1829,10 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
> 			stat(s, CPU_PARTIAL_NODE);
> 		}
> 		if (!kmem_cache_has_cpu_partial(s)
>-			|| available > s->cpu_partial / 2)
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
>+			|| available > s->cpu_partial / 2
>+#endif
>+			)
> 			break;

Matthew,

I plan to change this one with the same idea you mentioned in previous reply.

While one special "technique" is how to name it.

How about name this one

    slub_cpu_partial()

And rename the previous one

   slub_percpu_partial()

This is really hard to say which one is better :-(
Not sure whether you have some insight in this.

> 
> 	}
>@@ -3418,6 +3421,39 @@ static void set_min_partial(struct kmem_cache *s, unsigned long min)
> 	s->min_partial = min;
> }
> 
>+static void set_cpu_partial(struct kmem_cache *s)
>+{
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
>+	/*
>+	 * cpu_partial determined the maximum number of objects kept in the
>+	 * per cpu partial lists of a processor.
>+	 *
>+	 * Per cpu partial lists mainly contain slabs that just have one
>+	 * object freed. If they are used for allocation then they can be
>+	 * filled up again with minimal effort. The slab will never hit the
>+	 * per node partial lists and therefore no locking will be required.
>+	 *
>+	 * This setting also determines
>+	 *
>+	 * A) The number of objects from per cpu partial slabs dumped to the
>+	 *    per node list when we reach the limit.
>+	 * B) The number of objects in cpu partial slabs to extract from the
>+	 *    per node list when we run out of per cpu objects. We only fetch
>+	 *    50% to keep some capacity around for frees.
>+	 */
>+	if (!kmem_cache_has_cpu_partial(s))
>+		s->cpu_partial = 0;
>+	else if (s->size >= PAGE_SIZE)
>+		s->cpu_partial = 2;
>+	else if (s->size >= 1024)
>+		s->cpu_partial = 6;
>+	else if (s->size >= 256)
>+		s->cpu_partial = 13;
>+	else
>+		s->cpu_partial = 30;
>+#endif
>+}
>+
> /*
>  * calculate_sizes() determines the order and the distribution of data within
>  * a slab object.
>@@ -3576,33 +3612,7 @@ static int kmem_cache_open(struct kmem_cache *s, unsigned long flags)
> 	 */
> 	set_min_partial(s, ilog2(s->size) / 2);
> 
>-	/*
>-	 * cpu_partial determined the maximum number of objects kept in the
>-	 * per cpu partial lists of a processor.
>-	 *
>-	 * Per cpu partial lists mainly contain slabs that just have one
>-	 * object freed. If they are used for allocation then they can be
>-	 * filled up again with minimal effort. The slab will never hit the
>-	 * per node partial lists and therefore no locking will be required.
>-	 *
>-	 * This setting also determines
>-	 *
>-	 * A) The number of objects from per cpu partial slabs dumped to the
>-	 *    per node list when we reach the limit.
>-	 * B) The number of objects in cpu partial slabs to extract from the
>-	 *    per node list when we run out of per cpu objects. We only fetch
>-	 *    50% to keep some capacity around for frees.
>-	 */
>-	if (!kmem_cache_has_cpu_partial(s))
>-		s->cpu_partial = 0;
>-	else if (s->size >= PAGE_SIZE)
>-		s->cpu_partial = 2;
>-	else if (s->size >= 1024)
>-		s->cpu_partial = 6;
>-	else if (s->size >= 256)
>-		s->cpu_partial = 13;
>-	else
>-		s->cpu_partial = 30;
>+	set_cpu_partial(s);
> 
> #ifdef CONFIG_NUMA
> 	s->remote_node_defrag_ratio = 1000;
>@@ -3989,7 +3999,9 @@ void __kmemcg_cache_deactivate(struct kmem_cache *s)
> 	 * Disable empty slabs caching. Used to avoid pinning offline
> 	 * memory cgroups by kmem pages that can be freed.
> 	 */
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> 	s->cpu_partial = 0;
>+#endif
> 	s->min_partial = 0;
> 
> 	/*
>@@ -4929,6 +4941,7 @@ static ssize_t min_partial_store(struct kmem_cache *s, const char *buf,
> }
> SLAB_ATTR(min_partial);
> 
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> static ssize_t cpu_partial_show(struct kmem_cache *s, char *buf)
> {
> 	return sprintf(buf, "%u\n", s->cpu_partial);
>@@ -4951,6 +4964,7 @@ static ssize_t cpu_partial_store(struct kmem_cache *s, const char *buf,
> 	return length;
> }
> SLAB_ATTR(cpu_partial);
>+#endif
> 
> static ssize_t ctor_show(struct kmem_cache *s, char *buf)
> {
>@@ -5363,7 +5377,9 @@ static struct attribute *slab_attrs[] = {
> 	&objs_per_slab_attr.attr,
> 	&order_attr.attr,
> 	&min_partial_attr.attr,
>+#ifdef CONFIG_SLUB_CPU_PARTIAL
> 	&cpu_partial_attr.attr,
>+#endif
> 	&objects_attr.attr,
> 	&objects_partial_attr.attr,
> 	&partial_attr.attr,
>-- 
>2.11.0

-- 
Wei Yang
Help you, Help me

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Re: [PATCH 0/3] try to save some memory for kmem_cache in some cases

[Christoph Lameter]

On Sun, 30 Apr 2017, Wei Yang wrote:

> kmem_cache is a frequently used data in kernel. During the code reading, I
> found maybe we could save some space in some cases.
>
> 1. On 64bit arch, type int will occupy a word if it doesn't sit well.
> 2. cpu_slab->partial is just used when CONFIG_SLUB_CPU_PARTIAL is set
> 3. cpu_partial is just used when CONFIG_SLUB_CPU_PARTIAL is set, while just
> save some space on 32bit arch.

This looks fine. But do we really want to add that amount of ifdeffery?
How much memory does this save?