[PATCH v2 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting

[PATCH v2 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting

[Wanpeng Li]

Changelog:
 * add comments from Andi which indicate shrink gigantic hugetlb page pools make 
   sense to patchset description.

order >= MAX_ORDER pages are only allocated at boot stage using the 
bootmem allocator with the "hugepages=xxx" option. These pages are never 
free after boot by default since it would be a one-way street(>= MAX_ORDER
pages cannot be allocated later), but if administrator confirm not to 
use these gigantic pages any more, these pinned pages will waste memory
since other users can't grab free pages from gigantic hugetlb pool even
if OOM, it's not flexible.  The patchset add hugetlb gigantic page pools
shrink supporting. Administrator can enable knob exported in sysctl to
permit to shrink gigantic hugetlb pool.

http://marc.info/?l=linux-mm&m=136578016214512&w=2 
Andi thinks this idea make sense since he is working on a new patchkit to 
allocate GB pages from CMA. With that freeing actually makes sense, as the 
pages can be reallocated.

Testcase:
boot: hugepagesz=1G hugepages=10

[root@localhost hugepages]# free -m
             total       used       free     shared    buffers     cached
Mem:         36269      10836      25432          0         11        288
-/+ buffers/cache:      10537      25732
Swap:        35999          0      35999
[root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
-bash: echo: write error: Invalid argument
[root@localhost hugepages]# echo 1 > /proc/sys/vm/hugetlb_shrink_gigantic_pool
[root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
[root@localhost hugepages]# free -m
             total       used       free     shared    buffers     cached
Mem:         36269        597      35672          0         11        288
-/+ buffers/cache:        297      35972
Swap:        35999          0      35999

Wanpeng Li (6):
  introduce new sysctl knob which control gigantic page pools shrinking
  update_and_free_page gigantic pages awareness
  enable gigantic hugetlb page pools shrinking
  use already exist huge_page_order() instead of h->order
  remove redundant hugetlb_prefault 
  use already exist interface huge_page_shift

 Documentation/sysctl/vm.txt |   13 +++++++
 include/linux/hugetlb.h     |    5 +--
 kernel/sysctl.c             |    7 ++++
 mm/hugetlb.c                |   83 +++++++++++++++++++++++++++++--------------
 mm/internal.h               |    1 +
 mm/page_alloc.c             |    2 +-
 6 files changed, 82 insertions(+), 29 deletions(-)

-- 
1.7.10.4

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[PATCH v2 1/6] mm/hugetlb: introduce new sysctl knob which control gigantic page pools shrinking

[Wanpeng Li]

This patch introduces new sysctl knob to support gigantic hugetlb page
pools shrinking. The default value is 0 since gigantic page pools
aren't permitted shrinked by default, administrator can echo 1 to knob
to enable gigantic page pools shrinking after they confirm they won't
use them any more.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 Documentation/sysctl/vm.txt |   13 +++++++++++++
 include/linux/hugetlb.h     |    3 +++
 kernel/sysctl.c             |    7 +++++++
 mm/hugetlb.c                |    9 +++++++++
 4 files changed, 32 insertions(+)

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 21ad181..3baf332 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -30,6 +30,7 @@ Currently, these files are in /proc/sys/vm:
 - extfrag_threshold
 - hugepages_treat_as_movable
 - hugetlb_shm_group
+- hugetlb_shrink_gigantic_pool
 - laptop_mode
 - legacy_va_layout
 - lowmem_reserve_ratio
@@ -211,6 +212,18 @@ shared memory segment using hugetlb page.
 
 ==============================================================
 
+hugetlb_shrink_gigantic_pool
+
+order >= MAX_ORDER pages are only allocated at boot stage using the bootmem
+allocator with the "hugepages=xxx" option. These pages are never free'd
+by default since it would be a one-way street(>= MAX_ORDER pages cannot
+be allocated later), but if administrator confirm not to use these gigantic
+pages any more, these pinned pages will waste memory since other users
+can't grab free pages from gigantic hugetlb pool even OOM. Administrator
+can enable this parameter to permit to shrink gigantic hugetlb pool
+
+==============================================================
+
 laptop_mode
 
 laptop_mode is a knob that controls "laptop mode". All the things that are
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 3a62df3..b7e4106 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -36,6 +36,8 @@ void reset_vma_resv_huge_pages(struct vm_area_struct *vma);
 int hugetlb_sysctl_handler(struct ctl_table *, int, void __user *, size_t *, loff_t *);
 int hugetlb_overcommit_handler(struct ctl_table *, int, void __user *, size_t *, loff_t *);
 int hugetlb_treat_movable_handler(struct ctl_table *, int, void __user *, size_t *, loff_t *);
+int hugetlb_shrink_gigantic_pool_handler(struct ctl_table *,
+				int, void __user *, size_t *, loff_t *);
 
 #ifdef CONFIG_NUMA
 int hugetlb_mempolicy_sysctl_handler(struct ctl_table *, int,
@@ -73,6 +75,7 @@ extern unsigned long hugepages_treat_as_movable;
 extern const unsigned long hugetlb_zero, hugetlb_infinity;
 extern int sysctl_hugetlb_shm_group;
 extern struct list_head huge_boot_pages;
+extern int hugetlb_shrink_gigantic_pool;
 
 /* arch callbacks */
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 3dadde5..25eb85f 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1187,6 +1187,13 @@ static struct ctl_table vm_table[] = {
 		.extra1		= (void *)&hugetlb_zero,
 		.extra2		= (void *)&hugetlb_infinity,
 	},
+	{
+		.procname       = "hugetlb_shrink_gigantic_pool",
+		.data           = &hugetlb_shrink_gigantic_pool,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = hugetlb_shrink_gigantic_pool_handler,
+	},
 #ifdef CONFIG_NUMA
 	{
 		.procname       = "nr_hugepages_mempolicy",
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index bacdf38..4a0c270 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -35,6 +35,7 @@
 const unsigned long hugetlb_zero = 0, hugetlb_infinity = ~0UL;
 static gfp_t htlb_alloc_mask = GFP_HIGHUSER;
 unsigned long hugepages_treat_as_movable;
+int hugetlb_shrink_gigantic_pool;
 
 int hugetlb_max_hstate __read_mostly;
 unsigned int default_hstate_idx;
@@ -671,6 +672,14 @@ static void prep_compound_gigantic_page(struct page *page, unsigned long order)
 	}
 }
 
+int hugetlb_shrink_gigantic_pool_handler(struct ctl_table *table, int write,
+			void __user *buffer,
+			size_t *length, loff_t *ppos)
+{
+	proc_dointvec(table, write, buffer, length, ppos);
+	return 0;
+}
+
 /*
  * PageHuge() only returns true for hugetlbfs pages, but not for normal or
  * transparent huge pages.  See the PageTransHuge() documentation for more
-- 
1.7.10.4

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[PATCH v2 2/6] mm/hugetlb: update_and_free_page gigantic pages awareness

[Wanpeng Li]

order >= MAX_ORDER pages can't be freed to buddy system directly, this patch
destroy the gigantic hugetlb page to normal order-0 pages and free them one
by one.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/hugetlb.c    |   39 +++++++++++++++++++++++++++++----------
 mm/internal.h   |    1 +
 mm/page_alloc.c |    2 +-
 3 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 4a0c270..eeaf6f2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -579,25 +579,44 @@ err:
 	return NULL;
 }
 
+static inline clear_page_flag(struct page *page)
+{
+	page->flags &= ~(1 << PG_locked | 1 << PG_error |
+		1 << PG_referenced | 1 << PG_dirty |
+		1 << PG_active | 1 << PG_reserved |
+		1 << PG_private | 1 << PG_writeback);
+}
+
 static void update_and_free_page(struct hstate *h, struct page *page)
 {
 	int i;
+	struct page *p;
+	int order = huge_page_order(h);
 
-	VM_BUG_ON(h->order >= MAX_ORDER);
+	VM_BUG_ON(!hugetlb_shrink_gigantic_pool && h->order >= MAX_ORDER);
 
 	h->nr_huge_pages--;
 	h->nr_huge_pages_node[page_to_nid(page)]--;
-	for (i = 0; i < pages_per_huge_page(h); i++) {
-		page[i].flags &= ~(1 << PG_locked | 1 << PG_error |
-				1 << PG_referenced | 1 << PG_dirty |
-				1 << PG_active | 1 << PG_reserved |
-				1 << PG_private | 1 << PG_writeback);
-	}
-	VM_BUG_ON(hugetlb_cgroup_from_page(page));
 	set_compound_page_dtor(page, NULL);
-	set_page_refcounted(page);
 	arch_release_hugepage(page);
-	__free_pages(page, huge_page_order(h));
+	VM_BUG_ON(hugetlb_cgroup_from_page(page));
+
+	if (order < MAX_ORDER) {
+		for (i = 0; i < pages_per_huge_page(h); i++)
+			clear_page_flag(page+i);
+		set_page_refcounted(page);
+		__free_pages(page, huge_page_order(h));
+	} else {
+		int nr_pages = 1 << order;
+		destroy_compound_page(page, order);
+		set_compound_order(page, 0);
+		for (i = 0, p = page; i < nr_pages; i++,
+					p = mem_map_next(p, page, i)) {
+			clear_page_flag(p);
+			set_page_refcounted(p);
+			__free_pages(p, 0);
+		}
+	}
 }
 
 struct hstate *size_to_hstate(unsigned long size)
diff --git a/mm/internal.h b/mm/internal.h
index 8562de0..a63a35f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -101,6 +101,7 @@ extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address);
  */
 extern void __free_pages_bootmem(struct page *page, unsigned int order);
 extern void prep_compound_page(struct page *page, unsigned long order);
+extern int destroy_compound_page(struct page *page, unsigned long order);
 #ifdef CONFIG_MEMORY_FAILURE
 extern bool is_free_buddy_page(struct page *page);
 #endif
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 1394c5a..0ea14ba 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -367,7 +367,7 @@ void prep_compound_page(struct page *page, unsigned long order)
 }
 
 /* update __split_huge_page_refcount if you change this function */
-static int destroy_compound_page(struct page *page, unsigned long order)
+int destroy_compound_page(struct page *page, unsigned long order)
 {
 	int i;
 	int nr_pages = 1 << order;
-- 
1.7.10.4

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[PATCH v2 3/6] mm/hugetlb: enable gigantic hugetlb page pools shrinking

[Wanpeng Li]

Enable gigantic hugetlb page pools shrinking.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/hugetlb.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index eeaf6f2..328f140 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1416,7 +1416,8 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
 {
 	unsigned long min_count, ret;
 
-	if (h->order >= MAX_ORDER)
+	if (h->order >= MAX_ORDER && (!hugetlb_shrink_gigantic_pool ||
+				count > persistent_huge_pages(h)))
 		return h->max_huge_pages;
 
 	/*
@@ -1542,7 +1543,7 @@ static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
 		goto out;
 
 	h = kobj_to_hstate(kobj, &nid);
-	if (h->order >= MAX_ORDER) {
+	if (h->order >= MAX_ORDER && !hugetlb_shrink_gigantic_pool) {
 		err = -EINVAL;
 		goto out;
 	}
@@ -2036,7 +2037,7 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
 
 	tmp = h->max_huge_pages;
 
-	if (write && h->order >= MAX_ORDER)
+	if (write && h->order >= MAX_ORDER && !hugetlb_shrink_gigantic_pool)
 		return -EINVAL;
 
 	table->data = &tmp;
-- 
1.7.10.4

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[PATCH v2 4/6] mm/hugetlb: use already exist huge_page_order() instead of h->order

[Wanpeng Li]

Use already exist interface huge_page_order() instead of h->order to get 
huge page order.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/hugetlb.c |   36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 328f140..0cae950 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -593,7 +593,8 @@ static void update_and_free_page(struct hstate *h, struct page *page)
 	struct page *p;
 	int order = huge_page_order(h);
 
-	VM_BUG_ON(!hugetlb_shrink_gigantic_pool && h->order >= MAX_ORDER);
+	VM_BUG_ON(!hugetlb_shrink_gigantic_pool &&
+					huge_page_order(h) >= MAX_ORDER);
 
 	h->nr_huge_pages--;
 	h->nr_huge_pages_node[page_to_nid(page)]--;
@@ -722,7 +723,7 @@ static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
 {
 	struct page *page;
 
-	if (h->order >= MAX_ORDER)
+	if (huge_page_order(h) >= MAX_ORDER)
 		return NULL;
 
 	page = alloc_pages_exact_node(nid,
@@ -876,7 +877,7 @@ static struct page *alloc_buddy_huge_page(struct hstate *h, int nid)
 	struct page *page;
 	unsigned int r_nid;
 
-	if (h->order >= MAX_ORDER)
+	if (huge_page_order(h) >= MAX_ORDER)
 		return NULL;
 
 	/*
@@ -1071,7 +1072,7 @@ static void return_unused_surplus_pages(struct hstate *h,
 	h->resv_huge_pages -= unused_resv_pages;
 
 	/* Cannot return gigantic pages currently */
-	if (h->order >= MAX_ORDER)
+	if (huge_page_order(h) >= MAX_ORDER)
 		return;
 
 	nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
@@ -1265,7 +1266,7 @@ static void __init gather_bootmem_prealloc(void)
 #endif
 		__ClearPageReserved(page);
 		WARN_ON(page_count(page) != 1);
-		prep_compound_huge_page(page, h->order);
+		prep_compound_huge_page(page, huge_page_order(h));
 		prep_new_huge_page(h, page, page_to_nid(page));
 		/*
 		 * If we had gigantic hugepages allocated at boot time, we need
@@ -1273,8 +1274,8 @@ static void __init gather_bootmem_prealloc(void)
 		 * fix confusing memory reports from free(1) and another
 		 * side-effects, like CommitLimit going negative.
 		 */
-		if (h->order > (MAX_ORDER - 1))
-			totalram_pages += 1 << h->order;
+		if (huge_page_order(h) > (MAX_ORDER - 1))
+			totalram_pages += 1 << huge_page_order(h);
 	}
 }
 
@@ -1283,7 +1284,7 @@ static void __init hugetlb_hstate_alloc_pages(struct hstate *h)
 	unsigned long i;
 
 	for (i = 0; i < h->max_huge_pages; ++i) {
-		if (h->order >= MAX_ORDER) {
+		if (huge_page_order(h) >= MAX_ORDER) {
 			if (!alloc_bootmem_huge_page(h))
 				break;
 		} else if (!alloc_fresh_huge_page(h,
@@ -1299,7 +1300,7 @@ static void __init hugetlb_init_hstates(void)
 
 	for_each_hstate(h) {
 		/* oversize hugepages were init'ed in early boot */
-		if (h->order < MAX_ORDER)
+		if (huge_page_order(h) < MAX_ORDER)
 			hugetlb_hstate_alloc_pages(h);
 	}
 }
@@ -1333,7 +1334,7 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
 {
 	int i;
 
-	if (h->order >= MAX_ORDER)
+	if (huge_page_order(h) >= MAX_ORDER)
 		return;
 
 	for_each_node_mask(i, *nodes_allowed) {
@@ -1416,8 +1417,8 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
 {
 	unsigned long min_count, ret;
 
-	if (h->order >= MAX_ORDER && (!hugetlb_shrink_gigantic_pool ||
-				count > persistent_huge_pages(h)))
+	if (huge_page_order(h) >= MAX_ORDER && (!hugetlb_shrink_gigantic_pool
+				|| count > persistent_huge_pages(h)))
 		return h->max_huge_pages;
 
 	/*
@@ -1543,7 +1544,7 @@ static ssize_t nr_hugepages_store_common(bool obey_mempolicy,
 		goto out;
 
 	h = kobj_to_hstate(kobj, &nid);
-	if (h->order >= MAX_ORDER && !hugetlb_shrink_gigantic_pool) {
+	if (huge_page_order(h) >= MAX_ORDER && !hugetlb_shrink_gigantic_pool) {
 		err = -EINVAL;
 		goto out;
 	}
@@ -1626,7 +1627,7 @@ static ssize_t nr_overcommit_hugepages_store(struct kobject *kobj,
 	unsigned long input;
 	struct hstate *h = kobj_to_hstate(kobj, NULL);
 
-	if (h->order >= MAX_ORDER)
+	if (huge_page_order(h) >= MAX_ORDER)
 		return -EINVAL;
 
 	err = strict_strtoul(buf, 10, &input);
@@ -2037,7 +2038,8 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
 
 	tmp = h->max_huge_pages;
 
-	if (write && h->order >= MAX_ORDER && !hugetlb_shrink_gigantic_pool)
+	if (write && huge_page_order(h) >= MAX_ORDER &&
+						!hugetlb_shrink_gigantic_pool)
 		return -EINVAL;
 
 	table->data = &tmp;
@@ -2102,7 +2104,7 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write,
 
 	tmp = h->nr_overcommit_huge_pages;
 
-	if (write && h->order >= MAX_ORDER)
+	if (write && huge_page_order(h) >= MAX_ORDER)
 		return -EINVAL;
 
 	table->data = &tmp;
@@ -3093,7 +3095,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
 	flush_tlb_range(vma, start, end);
 	mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
 
-	return pages << h->order;
+	return pages << huge_page_order(h);
 }
 
 int hugetlb_reserve_pages(struct inode *inode,
-- 
1.7.10.4

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[PATCH v2 5/6] mm/hugetlb: remove redundant hugetlb_prefault

[Wanpeng Li]

hugetlb_prefault is not used by any users. This patch remove redundant 
hugetlb_prefault.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 include/linux/hugetlb.h |    2 --
 1 file changed, 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index b7e4106..813b265 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -57,7 +57,6 @@ void __unmap_hugepage_range_final(struct mmu_gather *tlb,
 void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
 				unsigned long start, unsigned long end,
 				struct page *ref_page);
-int hugetlb_prefault(struct address_space *, struct vm_area_struct *);
 void hugetlb_report_meminfo(struct seq_file *);
 int hugetlb_report_node_meminfo(int, char *);
 void hugetlb_show_meminfo(void);
@@ -113,7 +112,6 @@ static inline unsigned long hugetlb_total_pages(void)
 #define follow_hugetlb_page(m,v,p,vs,a,b,i,w)	({ BUG(); 0; })
 #define follow_huge_addr(mm, addr, write)	ERR_PTR(-EINVAL)
 #define copy_hugetlb_page_range(src, dst, vma)	({ BUG(); 0; })
-#define hugetlb_prefault(mapping, vma)		({ BUG(); 0; })
 static inline void hugetlb_report_meminfo(struct seq_file *m)
 {
 }
-- 
1.7.10.4

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[PATCH v2 6/6] mm/hugetlb: use already exist interface huge_page_shift

[Wanpeng Li]

Use already exist interface huge_page_shift instead of h->order + PAGE_SHIFT.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
---
 mm/hugetlb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0cae950..750ed8a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -320,7 +320,7 @@ unsigned long vma_kernel_pagesize(struct vm_area_struct *vma)
 
 	hstate = hstate_vma(vma);
 
-	return 1UL << (hstate->order + PAGE_SHIFT);
+	return 1UL << huge_page_shift(hstate);
 }
 EXPORT_SYMBOL_GPL(vma_kernel_pagesize);
 
-- 
1.7.10.4

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Re: [PATCH v2 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting

[Michal Hocko]

On Wed 17-04-13 08:36:28, Wanpeng Li wrote:
> Changelog:
>  * add comments from Andi which indicate shrink gigantic hugetlb page pools make 
>    sense to patchset description.
>
> order >= MAX_ORDER pages are only allocated at boot stage using the 
> bootmem allocator with the "hugepages=xxx" option. These pages are never 
> free after boot by default since it would be a one-way street(>= MAX_ORDER
> pages cannot be allocated later), but if administrator confirm not to 
> use these gigantic pages any more, these pinned pages will waste memory
> since other users can't grab free pages from gigantic hugetlb pool even
> if OOM, it's not flexible.  The patchset add hugetlb gigantic page pools
> shrink supporting. Administrator can enable knob exported in sysctl to
> permit to shrink gigantic hugetlb pool.
> 
> http://marc.info/?l=linux-mm&m=136578016214512&w=2 
> Andi thinks this idea make sense since he is working on a new patchkit to 
> allocate GB pages from CMA. With that freeing actually makes sense, as the 
> pages can be reallocated.

But that is not implemented yet...
 
> 
> Testcase:
> boot: hugepagesz=1G hugepages=10
> 
> [root@localhost hugepages]# free -m
>              total       used       free     shared    buffers     cached
> Mem:         36269      10836      25432          0         11        288
> -/+ buffers/cache:      10537      25732
> Swap:        35999          0      35999
> [root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
> -bash: echo: write error: Invalid argument
> [root@localhost hugepages]# echo 1 > /proc/sys/vm/hugetlb_shrink_gigantic_pool

I have asked that already but it didn't get answered. What is the reason
for an explicit knob to enable this? It just adds an additional code and
it doesn't make much sense to me to be honest.

[...]
-- 
Michal Hocko
SUSE Labs

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Re: [PATCH v2 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting

[Wanpeng Li]

On Tue, Apr 16, 2013 at 06:11:44PM -0700, Michal Hocko wrote:
>On Wed 17-04-13 08:36:28, Wanpeng Li wrote:
>> Changelog:
>>  * add comments from Andi which indicate shrink gigantic hugetlb page pools make 
>>    sense to patchset description.
>>
>> order >= MAX_ORDER pages are only allocated at boot stage using the 
>> bootmem allocator with the "hugepages=xxx" option. These pages are never 
>> free after boot by default since it would be a one-way street(>= MAX_ORDER
>> pages cannot be allocated later), but if administrator confirm not to 
>> use these gigantic pages any more, these pinned pages will waste memory
>> since other users can't grab free pages from gigantic hugetlb pool even
>> if OOM, it's not flexible.  The patchset add hugetlb gigantic page pools
>> shrink supporting. Administrator can enable knob exported in sysctl to
>> permit to shrink gigantic hugetlb pool.
>> 
>> http://marc.info/?l=linux-mm&m=136578016214512&w=2 
>> Andi thinks this idea make sense since he is working on a new patchkit to 
>> allocate GB pages from CMA. With that freeing actually makes sense, as the 
>> pages can be reallocated.
>
>But that is not implemented yet...
>
>> 
>> Testcase:
>> boot: hugepagesz=1G hugepages=10
>> 
>> [root@localhost hugepages]# free -m
>>              total       used       free     shared    buffers     cached
>> Mem:         36269      10836      25432          0         11        288
>> -/+ buffers/cache:      10537      25732
>> Swap:        35999          0      35999
>> [root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
>> -bash: echo: write error: Invalid argument
>> [root@localhost hugepages]# echo 1 > /proc/sys/vm/hugetlb_shrink_gigantic_pool
>
>I have asked that already but it didn't get answered. What is the reason
>for an explicit knob to enable this? It just adds an additional code and
>it doesn't make much sense to me to be honest.

Make sense to me, it seems that I don't need to add this redundant knob and
just let gigantic hugetlb pages pool shrink awareness after Andi's patchkit
merged. ;-)

Regards,
Wanpeng Li 

>
>[...]
>-- 
>Michal Hocko
>SUSE Labs

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Re: [PATCH v2 0/6] mm/hugetlb: gigantic hugetlb page pools shrink supporting

[Wanpeng Li]

On Tue, Apr 16, 2013 at 06:11:44PM -0700, Michal Hocko wrote:
>On Wed 17-04-13 08:36:28, Wanpeng Li wrote:
>> Changelog:
>>  * add comments from Andi which indicate shrink gigantic hugetlb page pools make 
>>    sense to patchset description.
>>
>> order >= MAX_ORDER pages are only allocated at boot stage using the 
>> bootmem allocator with the "hugepages=xxx" option. These pages are never 
>> free after boot by default since it would be a one-way street(>= MAX_ORDER
>> pages cannot be allocated later), but if administrator confirm not to 
>> use these gigantic pages any more, these pinned pages will waste memory
>> since other users can't grab free pages from gigantic hugetlb pool even
>> if OOM, it's not flexible.  The patchset add hugetlb gigantic page pools
>> shrink supporting. Administrator can enable knob exported in sysctl to
>> permit to shrink gigantic hugetlb pool.
>> 
>> http://marc.info/?l=linux-mm&m=136578016214512&w=2 
>> Andi thinks this idea make sense since he is working on a new patchkit to 
>> allocate GB pages from CMA. With that freeing actually makes sense, as the 
>> pages can be reallocated.
>
>But that is not implemented yet...
>
>> 
>> Testcase:
>> boot: hugepagesz=1G hugepages=10
>> 
>> [root@localhost hugepages]# free -m
>>              total       used       free     shared    buffers     cached
>> Mem:         36269      10836      25432          0         11        288
>> -/+ buffers/cache:      10537      25732
>> Swap:        35999          0      35999
>> [root@localhost hugepages]# echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
>> -bash: echo: write error: Invalid argument
>> [root@localhost hugepages]# echo 1 > /proc/sys/vm/hugetlb_shrink_gigantic_pool
>
>I have asked that already but it didn't get answered. What is the reason
>for an explicit knob to enable this? It just adds an additional code and
>it doesn't make much sense to me to be honest.

Make sense to me, it seems that I don't need to add this redundant knob and
just let gigantic hugetlb pages pool shrink awareness after Andi's patchkit
merged. ;-)

Regards,
Wanpeng Li 

>
>[...]
>-- 
>Michal Hocko
>SUSE Labs

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