memory_hotplug: Free pages as higher order

When free pages are done with higher order, time spend on coalescing pages by buddy allocator can be reduced. With section size of 256MB, hot add latency of a single section shows improvement from 50-60 ms to less than 1 ms, hence improving the hot add latency by 60%.

Modify external providers of online callback to align with the change.

Signed-off-by Arun KS <[email protected]>

---

Changes since RFC:
- Rebase.
- As suggested by Michal Hocko remove pages_per_block.
- Modifed external providers of online_page_callback.

RFC:
https://lore.kernel.org/patchwork/patch/984754/

---
 drivers/hv/hv_balloon.c        |  6 +++--
 drivers/xen/balloon.c          | 18 +++++++++++---
 include/linux/memory_hotplug.h |  2 +-
 mm/memory_hotplug.c            | 55 +++++++++++++++++++++++++++++++++---------
 4 files changed, 63 insertions(+), 18 deletions(-)

drivers/hv/hv_balloon.c +4 -2

index b1b7880..c5bc0b5 100644
@@ -771,7 +771,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
        }
 }
 
-static void hv_online_page(struct page *pg)
+static int hv_online_page(struct page *pg, unsigned int order)
 {
        struct hv_hotadd_state *has;
        unsigned long flags;

@@ -783,10 +783,12 @@ static void hv_online_page(struct page *pg)
                if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
                        continue;
 
-               hv_page_online_one(has, pg);
+               hv_bring_pgs_online(has, pfn, (1UL << order));
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
+
+       return 0;
 }
 
 static int pfn_covered(unsigned long start_pfn, unsigned long pfn_cnt)

drivers/xen/balloon.c +15 -3

index e12bb25..010cf4d 100644
@@ -390,8 +390,8 @@ static enum bp_state reserve_additional_memory(void)
 
        /*
         * add_memory_resource() will call online_pages() which in its turn
-        * will call xen_online_page() callback causing deadlock if we don't
-        * release balloon_mutex here. Unlocking here is safe because the
+        * will call xen_bring_pgs_online() callback causing deadlock if we
+        * don't release balloon_mutex here. Unlocking here is safe because the
         * callers drop the mutex before trying again.
         */
        mutex_unlock(&balloon_mutex);

@@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
        mutex_unlock(&balloon_mutex);
 }
 
+static int xen_bring_pgs_online(struct page *pg, unsigned int order)
+{
+       unsigned long i, size = (1 << order);
+       unsigned long start_pfn = page_to_pfn(pg);
+
+       pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
+       for (i = 0; i < size; i++)
+               xen_online_page(pfn_to_page(start_pfn + i));
+
+       return 0;
+}
+
 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 {
        if (val == MEM_ONLINE)

@@ -744,7 +756,7 @@ static int __init balloon_init(void)
        balloon_stats.max_retry_count = RETRY_UNLIMITED;
 
 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
-       set_online_page_callback(&xen_online_page);
+       set_online_page_callback(&xen_bring_pgs_online);
        register_memory_notifier(&xen_memory_nb);
        register_sysctl_table(xen_root);
 

include/linux/memory_hotplug.h +1 -1

index 34a2822..7b04c1d 100644
@@ -87,7 +87,7 @@ extern int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
        unsigned long *valid_start, unsigned long *valid_end);
 extern void __offline_isolated_pages(unsigned long, unsigned long);
 
-typedef void (*online_page_callback_t)(struct page *page);
+typedef int (*online_page_callback_t)(struct page *page, unsigned int order);
 
 extern int set_online_page_callback(online_page_callback_t callback);
 extern int restore_online_page_callback(online_page_callback_t callback);

mm/memory_hotplug.c +2 -2

index 38d94b7..24c2b8e 100644
@@ -47,7 +47,7 @@
  * and restore_online_page_callback() for generic callback restore.
  */
 
-static void generic_online_page(struct page *page);
+static int generic_online_page(struct page *page, unsigned int order);
 
 static online_page_callback_t online_page_callback = generic_online_page;
 static DEFINE_MUTEX(online_page_callback_lock);

@@ -655,26 +655,57 @@ void __online_page_free(struct page *page)
 }
 EXPORT_SYMBOL_GPL(__online_page_free);
 
-static void generic_online_page(struct page *page)
+static int generic_online_page(struct page *page, unsigned int order)
 {

Quoted 147 lines · Arun KS

When free pages are done with higher order, time spend on coalescing pages by buddy allocator can be reduced. With section size of 256MB, hot add latency of a single section shows improvement from 50-60 ms to less than 1 ms, hence improving the hot add latency by 60%.

Modify external providers of online callback to align with the change.

Signed-off-by Arun KS <[email protected]>

---

Changes since RFC:
- Rebase.
- As suggested by Michal Hocko remove pages_per_block.
- Modifed external providers of online_page_callback.

RFC:
https://lore.kernel.org/patchwork/patch/984754/

---
 drivers/hv/hv_balloon.c        |  6 +++--
 drivers/xen/balloon.c          | 18 +++++++++++---
 include/linux/memory_hotplug.h |  2 +-
 mm/memory_hotplug.c            | 55 
+++++++++++++++++++++++++++++++++---------
 4 files changed, 63 insertions(+), 18 deletions(-)

drivers/hv/hv_balloon.c +1 -1

index b1b7880..c5bc0b5 100644
@@ -771,7 +771,7 @@ static void hv_mem_hot_add(unsigned long start, 
 unsigned long size,
        }
 }
 
-static void hv_online_page(struct page *pg)
+static int hv_online_page(struct page *pg, unsigned int order)
 {
        struct hv_hotadd_state *has;

        unsigned long flags;

drivers/hv/hv_balloon.c +3 -1

@@ -783,10 +783,12 @@ static void hv_online_page(struct page *pg)
                if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
                        continue;
 
-               hv_page_online_one(has, pg);
+               hv_bring_pgs_online(has, pfn, (1UL << order));
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
+
+       return 0;
 }
 
 static int pfn_covered(unsigned long start_pfn, unsigned long 

pfn_cnt)

drivers/xen/balloon.c +0 -0

index e12bb25..010cf4d 100644
@@ -390,8 +390,8 @@ static enum bp_state 
 reserve_additional_memory(void)
 
        /*
         * add_memory_resource() will call online_pages() which in its 

turn
- * will call xen_online_page() callback causing deadlock if we
don't
- * release balloon_mutex here. Unlocking here is safe because
the
+ * will call xen_bring_pgs_online() callback causing deadlock
if we
+ * don't release balloon_mutex here. Unlocking here is safe
because the

         * callers drop the mutex before trying again.
         */
        mutex_unlock(&balloon_mutex);

drivers/xen/balloon.c +12 -0

@@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
        mutex_unlock(&balloon_mutex);
 }
 
+static int xen_bring_pgs_online(struct page *pg, unsigned int order)
+{
+       unsigned long i, size = (1 << order);
+       unsigned long start_pfn = page_to_pfn(pg);
+
+       pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, 
 start_pfn);
+       for (i = 0; i < size; i++)
+               xen_online_page(pfn_to_page(start_pfn + i));
+
+       return 0;
+}
+
 static int xen_memory_notifier(struct notifier_block *nb, unsigned 
 long val, void *v)

 {
        if (val == MEM_ONLINE)

drivers/xen/balloon.c +1 -1

@@ -744,7 +756,7 @@ static int __init balloon_init(void)
        balloon_stats.max_retry_count = RETRY_UNLIMITED;
 
 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
-       set_online_page_callback(&xen_online_page);
+       set_online_page_callback(&xen_bring_pgs_online);
        register_memory_notifier(&xen_memory_nb);
        register_sysctl_table(xen_root);
 

include/linux/memory_hotplug.h +1 -1

index 34a2822..7b04c1d 100644
@@ -87,7 +87,7 @@ extern int test_pages_in_a_zone(unsigned long 
 start_pfn, unsigned long end_pfn,
        unsigned long *valid_start, unsigned long *valid_end);
 extern void __offline_isolated_pages(unsigned long, unsigned long);
 
-typedef void (*online_page_callback_t)(struct page *page);
+typedef int (*online_page_callback_t)(struct page *page, unsigned int 
 order);
 

extern int set_online_page_callback(online_page_callback_t callback); extern int restore_online_page_callback(online_page_callback_t
callback);

mm/memory_hotplug.c +1 -1

index 38d94b7..24c2b8e 100644
@@ -47,7 +47,7 @@
  * and restore_online_page_callback() for generic callback restore.
  */
 
-static void generic_online_page(struct page *page);
+static int generic_online_page(struct page *page, unsigned int 
 order);
 
 static online_page_callback_t online_page_callback = 

generic_online_page;
static DEFINE_MUTEX(online_page_callback_lock);

mm/memory_hotplug.c +1 -1

@@ -655,26 +655,57 @@ void __online_page_free(struct page *page)
 }
 EXPORT_SYMBOL_GPL(__online_page_free);
 
-static void generic_online_page(struct page *page)
+static int generic_online_page(struct page *page, unsigned int order)
 {

mm/memory_hotplug.c void __online_page_free(struct page *page) · line 666

Quoted 10 lines

mm/memory_hotplug.c +7 -3

-       __online_page_set_limits(page);
-       __online_page_increment_counters(page);
-       __online_page_free(page);
+       unsigned long nr_pages = 1 << order;
+       struct page *p = page;
+       unsigned int loop;
+
+       prefetchw(p);
+       for (loop = 0 ; loop < (nr_pages - 1) ; loop++, p++) {
+               prefetch(p + 1);

Given commits like:

e66eed651fd1 list: remove prefetching from regular list iterators 75d65a425c01 hlist: remove software prefetching in hlist iterators

...are you sure these explicit prefetch() calls are improving performance? My understanding is that hardware prefetchers don't need much help these days.

Quoted 147 lines · Arun KS

When free pages are done with higher order, time spend on coalescing pages by buddy allocator can be reduced. With section size of 256MB, hot add latency of a single section shows improvement from 50-60 ms to less than 1 ms, hence improving the hot add latency by 60%.

Modify external providers of online callback to align with the change.

Signed-off-by Arun KS <[email protected]>

---

Changes since RFC:
- Rebase.
- As suggested by Michal Hocko remove pages_per_block.
- Modifed external providers of online_page_callback.

RFC:
https://lore.kernel.org/patchwork/patch/984754/

---
 drivers/hv/hv_balloon.c        |  6 +++--
 drivers/xen/balloon.c          | 18 +++++++++++---
 include/linux/memory_hotplug.h |  2 +-
 mm/memory_hotplug.c            | 55 
+++++++++++++++++++++++++++++++++---------
 4 files changed, 63 insertions(+), 18 deletions(-)

drivers/hv/hv_balloon.c +1 -1

index b1b7880..c5bc0b5 100644
@@ -771,7 +771,7 @@ static void hv_mem_hot_add(unsigned long start, 
 unsigned long size,
        }
 }
 
-static void hv_online_page(struct page *pg)
+static int hv_online_page(struct page *pg, unsigned int order)
 {
        struct hv_hotadd_state *has;

        unsigned long flags;

drivers/hv/hv_balloon.c +3 -1

@@ -783,10 +783,12 @@ static void hv_online_page(struct page *pg)
                if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
                        continue;
 
-               hv_page_online_one(has, pg);
+               hv_bring_pgs_online(has, pfn, (1UL << order));
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
+
+       return 0;
 }
 
 static int pfn_covered(unsigned long start_pfn, unsigned long 

pfn_cnt)

drivers/xen/balloon.c +0 -0

index e12bb25..010cf4d 100644
@@ -390,8 +390,8 @@ static enum bp_state 
 reserve_additional_memory(void)
 
        /*
         * add_memory_resource() will call online_pages() which in its 

turn
- * will call xen_online_page() callback causing deadlock if we
don't
- * release balloon_mutex here. Unlocking here is safe because
the
+ * will call xen_bring_pgs_online() callback causing deadlock
if we
+ * don't release balloon_mutex here. Unlocking here is safe
because the

         * callers drop the mutex before trying again.
         */
        mutex_unlock(&balloon_mutex);

drivers/xen/balloon.c +12 -0

@@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
        mutex_unlock(&balloon_mutex);
 }
 
+static int xen_bring_pgs_online(struct page *pg, unsigned int order)
+{
+       unsigned long i, size = (1 << order);
+       unsigned long start_pfn = page_to_pfn(pg);
+
+       pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, 
 start_pfn);
+       for (i = 0; i < size; i++)
+               xen_online_page(pfn_to_page(start_pfn + i));
+
+       return 0;
+}
+
 static int xen_memory_notifier(struct notifier_block *nb, unsigned 
 long val, void *v)

 {
        if (val == MEM_ONLINE)

drivers/xen/balloon.c +1 -1

@@ -744,7 +756,7 @@ static int __init balloon_init(void)
        balloon_stats.max_retry_count = RETRY_UNLIMITED;
 
 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
-       set_online_page_callback(&xen_online_page);
+       set_online_page_callback(&xen_bring_pgs_online);
        register_memory_notifier(&xen_memory_nb);
        register_sysctl_table(xen_root);
 

include/linux/memory_hotplug.h +1 -1

index 34a2822..7b04c1d 100644
@@ -87,7 +87,7 @@ extern int test_pages_in_a_zone(unsigned long 
 start_pfn, unsigned long end_pfn,
        unsigned long *valid_start, unsigned long *valid_end);
 extern void __offline_isolated_pages(unsigned long, unsigned long);
 
-typedef void (*online_page_callback_t)(struct page *page);
+typedef int (*online_page_callback_t)(struct page *page, unsigned int 
 order);
 

extern int set_online_page_callback(online_page_callback_t callback); extern int restore_online_page_callback(online_page_callback_t
callback);

mm/memory_hotplug.c +1 -1

index 38d94b7..24c2b8e 100644
@@ -47,7 +47,7 @@
  * and restore_online_page_callback() for generic callback restore.
  */
 
-static void generic_online_page(struct page *page);
+static int generic_online_page(struct page *page, unsigned int 
 order);
 
 static online_page_callback_t online_page_callback = 

generic_online_page;
static DEFINE_MUTEX(online_page_callback_lock);

mm/memory_hotplug.c +1 -1

@@ -655,26 +655,57 @@ void __online_page_free(struct page *page)
 }
 EXPORT_SYMBOL_GPL(__online_page_free);
 
-static void generic_online_page(struct page *page)
+static int generic_online_page(struct page *page, unsigned int order)
 {

mm/memory_hotplug.c void __online_page_free(struct page *page) · line 666

Quoted 10 lines

mm/memory_hotplug.c +7 -3

-       __online_page_set_limits(page);
-       __online_page_increment_counters(page);
-       __online_page_free(page);
+       unsigned long nr_pages = 1 << order;
+       struct page *p = page;
+       unsigned int loop;
+
+       prefetchw(p);
+       for (loop = 0 ; loop < (nr_pages - 1) ; loop++, p++) {
+               prefetch(p + 1);

Given commits like:

e66eed651fd1 list: remove prefetching from regular list iterators 75d65a425c01 hlist: remove software prefetching in hlist iterators

...are you sure these explicit prefetch() calls are improving performance? My understanding is that hardware prefetchers don't need much help these days.

When free pages are done with higher order, time spend on coalescing pages by buddy allocator can be reduced. With section size of 256MB, hot add latency of a single section shows improvement from 50-60 ms to less than 1 ms, hence improving the hot add latency by 60%.

Modify external providers of online callback to align with the change.

Signed-off-by Arun KS <[email protected]>

---

Changes since RFC:
- Rebase.
- As suggested by Michal Hocko remove pages_per_block.
- Modifed external providers of online_page_callback.

RFC:
https://lore.kernel.org/patchwork/patch/984754/

---
 drivers/hv/hv_balloon.c        |  6 +++--
 drivers/xen/balloon.c          | 18 +++++++++++---
 include/linux/memory_hotplug.h |  2 +-
 mm/memory_hotplug.c            | 55 +++++++++++++++++++++++++++++++++---------
 4 files changed, 63 insertions(+), 18 deletions(-)

drivers/hv/hv_balloon.c +4 -2

index b1b7880..c5bc0b5 100644
@@ -771,7 +771,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
        }
 }
 
-static void hv_online_page(struct page *pg)
+static int hv_online_page(struct page *pg, unsigned int order)
 {
        struct hv_hotadd_state *has;
        unsigned long flags;

@@ -783,10 +783,12 @@ static void hv_online_page(struct page *pg)
                if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
                        continue;
 
-               hv_page_online_one(has, pg);
+               hv_bring_pgs_online(has, pfn, (1UL << order));
                break;
        }
        spin_unlock_irqrestore(&dm_device.ha_lock, flags);
+
+       return 0;
 }
 
 static int pfn_covered(unsigned long start_pfn, unsigned long pfn_cnt)

drivers/xen/balloon.c +15 -3

index e12bb25..010cf4d 100644
@@ -390,8 +390,8 @@ static enum bp_state reserve_additional_memory(void)
 
        /*
         * add_memory_resource() will call online_pages() which in its turn
-        * will call xen_online_page() callback causing deadlock if we don't
-        * release balloon_mutex here. Unlocking here is safe because the
+        * will call xen_bring_pgs_online() callback causing deadlock if we
+        * don't release balloon_mutex here. Unlocking here is safe because the
         * callers drop the mutex before trying again.
         */
        mutex_unlock(&balloon_mutex);

@@ -422,6 +422,18 @@ static void xen_online_page(struct page *page)
        mutex_unlock(&balloon_mutex);
 }
 
+static int xen_bring_pgs_online(struct page *pg, unsigned int order)
+{
+       unsigned long i, size = (1 << order);
+       unsigned long start_pfn = page_to_pfn(pg);
+
+       pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
+       for (i = 0; i < size; i++)
+               xen_online_page(pfn_to_page(start_pfn + i));
+
+       return 0;
+}
+
 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
 {
        if (val == MEM_ONLINE)

@@ -744,7 +756,7 @@ static int __init balloon_init(void)
        balloon_stats.max_retry_count = RETRY_UNLIMITED;
 
 #ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG
-       set_online_page_callback(&xen_online_page);
+       set_online_page_callback(&xen_bring_pgs_online);
        register_memory_notifier(&xen_memory_nb);
        register_sysctl_table(xen_root);
 

include/linux/memory_hotplug.h +1 -1

index 34a2822..7b04c1d 100644
@@ -87,7 +87,7 @@ extern int test_pages_in_a_zone(unsigned long start_pfn, unsigned long end_pfn,
        unsigned long *valid_start, unsigned long *valid_end);
 extern void __offline_isolated_pages(unsigned long, unsigned long);
 
-typedef void (*online_page_callback_t)(struct page *page);
+typedef int (*online_page_callback_t)(struct page *page, unsigned int order);
 
 extern int set_online_page_callback(online_page_callback_t callback);
 extern int restore_online_page_callback(online_page_callback_t callback);

mm/memory_hotplug.c +2 -2

index 38d94b7..24c2b8e 100644
@@ -47,7 +47,7 @@
  * and restore_online_page_callback() for generic callback restore.
  */
 
-static void generic_online_page(struct page *page);
+static int generic_online_page(struct page *page, unsigned int order);
 
 static online_page_callback_t online_page_callback = generic_online_page;
 static DEFINE_MUTEX(online_page_callback_lock);

@@ -655,26 +655,57 @@ void __online_page_free(struct page *page)
 }
 EXPORT_SYMBOL_GPL(__online_page_free);
 
-static void generic_online_page(struct page *page)
+static int generic_online_page(struct page *page, unsigned int order)
 {