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* [PATCH v5 1/2] memory_hotplug: Free pages as higher order
@ 2018-10-05  8:10 Arun KS
  2018-10-05  8:10 ` [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core Arun KS
                   ` (4 more replies)
  0 siblings, 5 replies; 25+ messages in thread
From: Arun KS @ 2018-10-05  8:10 UTC (permalink / raw)
  To: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, vbabka, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel
  Cc: vatsa, vinmenon, getarunks, 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 <arunks@codeaurora.org>
---
Changes since v4:
- As suggested by Michal Hocko,
- Simplify logic in online_pages_block() by using get_order().
- Seperate out removal of prefetch from __free_pages_core().

Changes since v3:
- Renamed _free_pages_boot_core -> __free_pages_core.
- Removed prefetch from __free_pages_core.
- Removed xen_online_page().

Changes since v2:
- Reuse code from __free_pages_boot_core().

Changes since v1:
- Removed prefetch().

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

v4: https://lore.kernel.org/patchwork/patch/995111/
v3: https://lore.kernel.org/patchwork/patch/992348/
v2: https://lore.kernel.org/patchwork/patch/991363/
v1: https://lore.kernel.org/patchwork/patch/989445/
RFC: https://lore.kernel.org/patchwork/patch/984754/

---
 drivers/hv/hv_balloon.c        |  6 ++++--
 drivers/xen/balloon.c          | 23 +++++++++++++++--------
 include/linux/memory_hotplug.h |  2 +-
 mm/internal.h                  |  1 +
 mm/memory_hotplug.c            | 42 ++++++++++++++++++++++++++++++------------
 mm/page_alloc.c                |  8 ++++----
 6 files changed, 55 insertions(+), 27 deletions(-)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index b1b7880..c5bc0b5 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -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)
diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
index e12bb25..58ddf48 100644
--- a/drivers/xen/balloon.c
+++ b/drivers/xen/balloon.c
@@ -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);
@@ -411,15 +411,22 @@ static enum bp_state reserve_additional_memory(void)
 	return BP_ECANCELED;
 }
 
-static void xen_online_page(struct page *page)
+static int xen_bring_pgs_online(struct page *pg, unsigned int order)
 {
-	__online_page_set_limits(page);
+	unsigned long i, size = (1 << order);
+	unsigned long start_pfn = page_to_pfn(pg);
+	struct page *p;
 
+	pr_debug("Online %lu pages starting at pfn 0x%lx\n", size, start_pfn);
 	mutex_lock(&balloon_mutex);
-
-	__balloon_append(page);
-
+	for (i = 0; i < size; i++) {
+		p = pfn_to_page(start_pfn + i);
+		__online_page_set_limits(p);
+		__balloon_append(p);
+	}
 	mutex_unlock(&balloon_mutex);
+
+	return 0;
 }
 
 static int xen_memory_notifier(struct notifier_block *nb, unsigned long val, void *v)
@@ -744,7 +751,7 @@ 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);
 
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 34a2822..7b04c1d 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -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);
diff --git a/mm/internal.h b/mm/internal.h
index 87256ae..636679c 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -163,6 +163,7 @@ static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn,
 extern int __isolate_free_page(struct page *page, unsigned int order);
 extern void __free_pages_bootmem(struct page *page, unsigned long pfn,
 					unsigned int order);
+extern void __free_pages_core(struct page *page, unsigned int order);
 extern void prep_compound_page(struct page *page, unsigned int order);
 extern void post_alloc_hook(struct page *page, unsigned int order,
 					gfp_t gfp_flags);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 38d94b7..e379e85 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -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 +655,44 @@ 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)
 {
-	__online_page_set_limits(page);
-	__online_page_increment_counters(page);
-	__online_page_free(page);
+	__free_pages_core(page, order);
+	totalram_pages += (1UL << order);
+#ifdef CONFIG_HIGHMEM
+	if (PageHighMem(page))
+		totalhigh_pages += (1UL << order);
+#endif
+	return 0;
+}
+
+static int online_pages_blocks(unsigned long start, unsigned long nr_pages)
+{
+	unsigned long end = start + nr_pages;
+	int order, ret, onlined_pages = 0;
+
+	while (start < end) {
+		order = min(MAX_ORDER - 1,
+			get_order(PFN_PHYS(end) - PFN_PHYS(start)));
+
+		ret = (*online_page_callback)(pfn_to_page(start), order);
+		if (!ret)
+			onlined_pages += (1UL << order);
+		else if (ret > 0)
+			onlined_pages += ret;
+
+		start += (1UL << order);
+	}
+	return onlined_pages;
 }
 
 static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
 			void *arg)
 {
-	unsigned long i;
 	unsigned long onlined_pages = *(unsigned long *)arg;
-	struct page *page;
 
 	if (PageReserved(pfn_to_page(start_pfn)))
-		for (i = 0; i < nr_pages; i++) {
-			page = pfn_to_page(start_pfn + i);
-			(*online_page_callback)(page);
-			onlined_pages++;
-		}
+		onlined_pages = online_pages_blocks(start_pfn, nr_pages);
 
 	online_mem_sections(start_pfn, start_pfn + nr_pages);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 89d2a2a..7ab5274 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1252,7 +1252,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 	local_irq_restore(flags);
 }
 
-static void __init __free_pages_boot_core(struct page *page, unsigned int order)
+void __free_pages_core(struct page *page, unsigned int order)
 {
 	unsigned int nr_pages = 1 << order;
 	struct page *p = page;
@@ -1331,7 +1331,7 @@ void __init __free_pages_bootmem(struct page *page, unsigned long pfn,
 {
 	if (early_page_uninitialised(pfn))
 		return;
-	return __free_pages_boot_core(page, order);
+	return __free_pages_core(page, order);
 }
 
 /*
@@ -1421,14 +1421,14 @@ static void __init deferred_free_range(unsigned long pfn,
 	if (nr_pages == pageblock_nr_pages &&
 	    (pfn & (pageblock_nr_pages - 1)) == 0) {
 		set_pageblock_migratetype(page, MIGRATE_MOVABLE);
-		__free_pages_boot_core(page, pageblock_order);
+		__free_pages_core(page, pageblock_order);
 		return;
 	}
 
 	for (i = 0; i < nr_pages; i++, page++, pfn++) {
 		if ((pfn & (pageblock_nr_pages - 1)) == 0)
 			set_pageblock_migratetype(page, MIGRATE_MOVABLE);
-		__free_pages_boot_core(page, 0);
+		__free_pages_core(page, 0);
 	}
 }
 
-- 
1.9.1

^ permalink raw reply	[flat|nested] 25+ messages in thread

* [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core
  2018-10-05  8:10 [PATCH v5 1/2] memory_hotplug: Free pages as higher order Arun KS
@ 2018-10-05  8:10 ` Arun KS
  2018-10-09  9:30   ` Michal Hocko
  2018-10-10 16:36   ` Vlastimil Babka
  2018-10-08  7:34 ` [PATCH v5 1/2] memory_hotplug: Free pages as higher order Oscar Salvador
                   ` (3 subsequent siblings)
  4 siblings, 2 replies; 25+ messages in thread
From: Arun KS @ 2018-10-05  8:10 UTC (permalink / raw)
  To: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, vbabka, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel
  Cc: vatsa, vinmenon, getarunks, Arun KS

They not only increase the code footprint, they actually make things
slower rather than faster. Remove them as contemporary hardware doesn't
need any hint.

Suggested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Arun KS <arunks@codeaurora.org>
---
 mm/page_alloc.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7ab5274..90db431 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1258,14 +1258,10 @@ void __free_pages_core(struct page *page, unsigned int order)
 	struct page *p = page;
 	unsigned int loop;
 
-	prefetchw(p);
-	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
-		prefetchw(p + 1);
+	for (loop = 0; loop < nr_pages ; loop++, p++) {
 		__ClearPageReserved(p);
 		set_page_count(p, 0);
 	}
-	__ClearPageReserved(p);
-	set_page_count(p, 0);
 
 	page_zone(page)->managed_pages += nr_pages;
 	set_page_refcounted(page);
-- 
1.9.1

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-05  8:10 [PATCH v5 1/2] memory_hotplug: Free pages as higher order Arun KS
  2018-10-05  8:10 ` [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core Arun KS
@ 2018-10-08  7:34 ` Oscar Salvador
  2018-10-09  9:29 ` Michal Hocko
                   ` (2 subsequent siblings)
  4 siblings, 0 replies; 25+ messages in thread
From: Oscar Salvador @ 2018-10-08  7:34 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, vbabka, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On Fri, Oct 05, 2018 at 01:40:05PM +0530, Arun KS wrote:
> 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 <arunks@codeaurora.org>

Looks good to me.

Reviewed-by: Oscar Salvador <osalvador@suse.de>

Just one thing below:
  
> @@ -1331,7 +1331,7 @@ void __init __free_pages_bootmem(struct page *page, unsigned long pfn,
>  {
>  	if (early_page_uninitialised(pfn))
>  		return;
> -	return __free_pages_boot_core(page, order);
> +	return __free_pages_core(page, order);

__free_pages_core is void, so I guess we do not need that return there.
Probably the code generated is the same though.
-- 
Oscar Salvador
SUSE L3

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-05  8:10 [PATCH v5 1/2] memory_hotplug: Free pages as higher order Arun KS
  2018-10-05  8:10 ` [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core Arun KS
  2018-10-08  7:34 ` [PATCH v5 1/2] memory_hotplug: Free pages as higher order Oscar Salvador
@ 2018-10-09  9:29 ` Michal Hocko
  2018-10-09  9:54   ` Arun KS
  2018-10-10  8:07 ` Oscar Salvador
  2018-10-10 15:30 ` Vlastimil Babka
  4 siblings, 1 reply; 25+ messages in thread
From: Michal Hocko @ 2018-10-09  9:29 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, vbabka, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On Fri 05-10-18 13:40:05, Arun KS wrote:
> 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.

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks for your patience with all the resubmission.
-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core
  2018-10-05  8:10 ` [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core Arun KS
@ 2018-10-09  9:30   ` Michal Hocko
  2018-10-10 16:36   ` Vlastimil Babka
  1 sibling, 0 replies; 25+ messages in thread
From: Michal Hocko @ 2018-10-09  9:30 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, vbabka, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On Fri 05-10-18 13:40:06, Arun KS wrote:
> They not only increase the code footprint, they actually make things
> slower rather than faster. Remove them as contemporary hardware doesn't
> need any hint.

I agree with the change but it is much better to add some numbers
whenever arguing about performance impact.

> 
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Arun KS <arunks@codeaurora.org>
> ---
>  mm/page_alloc.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7ab5274..90db431 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1258,14 +1258,10 @@ void __free_pages_core(struct page *page, unsigned int order)
>  	struct page *p = page;
>  	unsigned int loop;
>  
> -	prefetchw(p);
> -	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> -		prefetchw(p + 1);
> +	for (loop = 0; loop < nr_pages ; loop++, p++) {
>  		__ClearPageReserved(p);
>  		set_page_count(p, 0);
>  	}
> -	__ClearPageReserved(p);
> -	set_page_count(p, 0);
>  
>  	page_zone(page)->managed_pages += nr_pages;
>  	set_page_refcounted(page);
> -- 
> 1.9.1
> 

-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-09  9:29 ` Michal Hocko
@ 2018-10-09  9:54   ` Arun KS
  2018-10-09 11:06     ` Michal Hocko
  0 siblings, 1 reply; 25+ messages in thread
From: Arun KS @ 2018-10-09  9:54 UTC (permalink / raw)
  To: Michal Hocko
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, vbabka, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On 2018-10-09 14:59, Michal Hocko wrote:
> On Fri 05-10-18 13:40:05, Arun KS wrote:
>> 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.
> 
> Acked-by: Michal Hocko <mhocko@suse.com>
> 
> Thanks for your patience with all the resubmission.

Hello Michal,

I got the below email few days back. Do I still need to resubmit the 
patch? or is it already on the way to merge?

Regards,
Arun

The patch titled
      Subject: mm/page_alloc.c: memory hotplug: free pages as higher 
order
has been added to the -mm tree.  Its filename is
      memory_hotplug-free-pages-as-higher-order.patch

This patch should soon appear at
     
http://ozlabs.org/~akpm/mmots/broken-out/memory_hotplug-free-pages-as-higher-order.patch
and later at
     
http://ozlabs.org/~akpm/mmotm/broken-out/memory_hotplug-free-pages-as-higher-order.patch

Before you just go and hit "reply", please:
    a) Consider who else should be cc'ed
    b) Prefer to cc a suitable mailing list as well
    c) Ideally: find the original patch on the mailing list and do a
       reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when 
testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-09  9:54   ` Arun KS
@ 2018-10-09 11:06     ` Michal Hocko
  0 siblings, 0 replies; 25+ messages in thread
From: Michal Hocko @ 2018-10-09 11:06 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, vbabka, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On Tue 09-10-18 15:24:13, Arun KS wrote:
> On 2018-10-09 14:59, Michal Hocko wrote:
> > On Fri 05-10-18 13:40:05, Arun KS wrote:
> > > 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.
> > 
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > 
> > Thanks for your patience with all the resubmission.
> 
> Hello Michal,
> 
> I got the below email few days back. Do I still need to resubmit the patch?
> or is it already on the way to merge?

It is sitting in the queue for now. Andrew collects acks and
reviewed-bys and add them to the patch.
-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-05  8:10 [PATCH v5 1/2] memory_hotplug: Free pages as higher order Arun KS
                   ` (2 preceding siblings ...)
  2018-10-09  9:29 ` Michal Hocko
@ 2018-10-10  8:07 ` Oscar Salvador
  2018-10-10 10:51   ` Arun KS
  2018-10-10 15:30 ` Vlastimil Babka
  4 siblings, 1 reply; 25+ messages in thread
From: Oscar Salvador @ 2018-10-10  8:07 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, vbabka, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On Fri, Oct 05, 2018 at 01:40:05PM +0530, Arun KS wrote:
> 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.

Hi Arun, out of curiosity:

could you please explain how exactly did you mesure the speed
improvement?

Thanks
-- 
Oscar Salvador
SUSE L3

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-10  8:07 ` Oscar Salvador
@ 2018-10-10 10:51   ` Arun KS
  2018-10-10 11:01     ` Oscar Salvador
  0 siblings, 1 reply; 25+ messages in thread
From: Arun KS @ 2018-10-10 10:51 UTC (permalink / raw)
  To: Oscar Salvador
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, vbabka, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On 2018-10-10 13:37, Oscar Salvador wrote:
> On Fri, Oct 05, 2018 at 01:40:05PM +0530, Arun KS wrote:
>> 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.
> 
> Hi Arun, out of curiosity:
> 
> could you please explain how exactly did you mesure the speed
> improvement?

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index e379e85..2416136 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -690,9 +690,13 @@ static int online_pages_range(unsigned long 
start_pfn, unsigned long nr_pages,
                         void *arg)
  {
         unsigned long onlined_pages = *(unsigned long *)arg;
+       u64 t1, t2;

+       t1 = local_clock();
         if (PageReserved(pfn_to_page(start_pfn)))
                 onlined_pages = online_pages_blocks(start_pfn, 
nr_pages);
+       t2 = local_clock();
+       trace_printk("time spend = %llu us\n", (t2-t1)/(1000));

         online_mem_sections(start_pfn, start_pfn + nr_pages);


Regards,
Arun

> 
> Thanks

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-10 10:51   ` Arun KS
@ 2018-10-10 11:01     ` Oscar Salvador
  0 siblings, 0 replies; 25+ messages in thread
From: Oscar Salvador @ 2018-10-10 11:01 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, vbabka, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On Wed, Oct 10, 2018 at 04:21:16PM +0530, Arun KS wrote:
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e379e85..2416136 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -690,9 +690,13 @@ static int online_pages_range(unsigned long start_pfn,
> unsigned long nr_pages,
>                         void *arg)
>  {
>         unsigned long onlined_pages = *(unsigned long *)arg;
> +       u64 t1, t2;
> 
> +       t1 = local_clock();
>         if (PageReserved(pfn_to_page(start_pfn)))
>                 onlined_pages = online_pages_blocks(start_pfn, nr_pages);
> +       t2 = local_clock();
> +       trace_printk("time spend = %llu us\n", (t2-t1)/(1000));
> 
>         online_mem_sections(start_pfn, start_pfn + nr_pages);

Thanks ;-)
 

-- 
Oscar Salvador
SUSE L3

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-05  8:10 [PATCH v5 1/2] memory_hotplug: Free pages as higher order Arun KS
                   ` (3 preceding siblings ...)
  2018-10-10  8:07 ` Oscar Salvador
@ 2018-10-10 15:30 ` Vlastimil Babka
  2018-10-10 16:56   ` Arun KS
  4 siblings, 1 reply; 25+ messages in thread
From: Vlastimil Babka @ 2018-10-10 15:30 UTC (permalink / raw)
  To: Arun KS, kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel
  Cc: vatsa, vinmenon, getarunks

On 10/5/18 10:10 AM, Arun KS wrote:
> 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 <arunks@codeaurora.org>

[...]

> @@ -655,26 +655,44 @@ 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)
>  {
> -	__online_page_set_limits(page);

This is now not called anymore, although the xen/hv variants still do
it. The function seems empty these days, maybe remove it as a followup
cleanup?

> -	__online_page_increment_counters(page);
> -	__online_page_free(page);
> +	__free_pages_core(page, order);
> +	totalram_pages += (1UL << order);
> +#ifdef CONFIG_HIGHMEM
> +	if (PageHighMem(page))
> +		totalhigh_pages += (1UL << order);
> +#endif

__online_page_increment_counters() would have used
adjust_managed_page_count() which would do the changes under
managed_page_count_lock. Are we safe without the lock? If yes, there
should perhaps be a comment explaining why.

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core
  2018-10-05  8:10 ` [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core Arun KS
  2018-10-09  9:30   ` Michal Hocko
@ 2018-10-10 16:36   ` Vlastimil Babka
  1 sibling, 0 replies; 25+ messages in thread
From: Vlastimil Babka @ 2018-10-10 16:36 UTC (permalink / raw)
  To: Arun KS, kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel
  Cc: vatsa, vinmenon, getarunks

On 10/5/18 10:10 AM, Arun KS wrote:
> They not only increase the code footprint, they actually make things
> slower rather than faster. Remove them as contemporary hardware doesn't
> need any hint.
> 
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Arun KS <arunks@codeaurora.org>

Yeah, a tight loop with fixed stride is a trivial case for hw prefetcher.

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/page_alloc.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 7ab5274..90db431 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1258,14 +1258,10 @@ void __free_pages_core(struct page *page, unsigned int order)
>  	struct page *p = page;
>  	unsigned int loop;
>  
> -	prefetchw(p);
> -	for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
> -		prefetchw(p + 1);
> +	for (loop = 0; loop < nr_pages ; loop++, p++) {
>  		__ClearPageReserved(p);
>  		set_page_count(p, 0);
>  	}
> -	__ClearPageReserved(p);
> -	set_page_count(p, 0);
>  
>  	page_zone(page)->managed_pages += nr_pages;
>  	set_page_refcounted(page);
> 

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-10 15:30 ` Vlastimil Babka
@ 2018-10-10 16:56   ` Arun KS
  2018-10-10 17:33     ` Michal Hocko
  2018-10-11  8:07     ` Vlastimil Babka
  0 siblings, 2 replies; 25+ messages in thread
From: Arun KS @ 2018-10-10 16:56 UTC (permalink / raw)
  To: Vlastimil Babka
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On 2018-10-10 21:00, Vlastimil Babka wrote:
> On 10/5/18 10:10 AM, Arun KS wrote:
>> 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 <arunks@codeaurora.org>
> 
> [...]
> 
>> @@ -655,26 +655,44 @@ 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)
>>  {
>> -	__online_page_set_limits(page);
> 
> This is now not called anymore, although the xen/hv variants still do
> it. The function seems empty these days, maybe remove it as a followup
> cleanup?
> 
>> -	__online_page_increment_counters(page);
>> -	__online_page_free(page);
>> +	__free_pages_core(page, order);
>> +	totalram_pages += (1UL << order);
>> +#ifdef CONFIG_HIGHMEM
>> +	if (PageHighMem(page))
>> +		totalhigh_pages += (1UL << order);
>> +#endif
> 
> __online_page_increment_counters() would have used
> adjust_managed_page_count() which would do the changes under
> managed_page_count_lock. Are we safe without the lock? If yes, there
> should perhaps be a comment explaining why.

Looks unsafe without managed_page_count_lock. I think better have a 
similar implementation of free_boot_core() in memory_hotplug.c like we 
had in version 1 of patch. And use adjust_managed_page_count() instead 
of page_zone(page)->managed_pages += nr_pages;

https://lore.kernel.org/patchwork/patch/989445/

-static void generic_online_page(struct page *page)
+static int generic_online_page(struct page *page, unsigned int order)
  {
-	__online_page_set_limits(page);
-	__online_page_increment_counters(page);
-	__online_page_free(page);
+	unsigned long nr_pages = 1 << order;
+	struct page *p = page;
+
+	for (loop = 0 ; loop < nr_pages ; loop++, p++) {
+		__ClearPageReserved(p);
+		set_page_count(p, 0);
+	}
+
+	adjust_managed_page_count(page, nr_pages);
+	set_page_refcounted(page);
+	__free_pages(page, order);
+
+	return 0;
+}


Regards,
Arun

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-10 16:56   ` Arun KS
@ 2018-10-10 17:33     ` Michal Hocko
  2018-10-11  2:29       ` Arun KS
  2018-10-11  8:07     ` Vlastimil Babka
  1 sibling, 1 reply; 25+ messages in thread
From: Michal Hocko @ 2018-10-10 17:33 UTC (permalink / raw)
  To: Arun KS
  Cc: Vlastimil Babka, kys, haiyangz, sthemmin, boris.ostrovsky,
	jgross, akpm, dan.j.williams, iamjoonsoo.kim, gregkh, osalvador,
	malat, kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman,
	aaron.lu, devel, linux-kernel, linux-mm, xen-devel, vatsa,
	vinmenon, getarunks

On Wed 10-10-18 22:26:41, Arun KS wrote:
> On 2018-10-10 21:00, Vlastimil Babka wrote:
> > On 10/5/18 10:10 AM, Arun KS wrote:
> > > 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 <arunks@codeaurora.org>
> > 
> > [...]
> > 
> > > @@ -655,26 +655,44 @@ 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)
> > >  {
> > > -	__online_page_set_limits(page);
> > 
> > This is now not called anymore, although the xen/hv variants still do
> > it. The function seems empty these days, maybe remove it as a followup
> > cleanup?
> > 
> > > -	__online_page_increment_counters(page);
> > > -	__online_page_free(page);
> > > +	__free_pages_core(page, order);
> > > +	totalram_pages += (1UL << order);
> > > +#ifdef CONFIG_HIGHMEM
> > > +	if (PageHighMem(page))
> > > +		totalhigh_pages += (1UL << order);
> > > +#endif
> > 
> > __online_page_increment_counters() would have used
> > adjust_managed_page_count() which would do the changes under
> > managed_page_count_lock. Are we safe without the lock? If yes, there
> > should perhaps be a comment explaining why.
> 
> Looks unsafe without managed_page_count_lock.

Why does it matter actually? We cannot online/offline memory in
parallel. This is not the case for the boot where we initialize memory
in parallel on multiple nodes. So this seems to be safe currently unless
I am missing something. A comment explaining that would be helpful
though.
-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-10 17:33     ` Michal Hocko
@ 2018-10-11  2:29       ` Arun KS
  2018-10-11  7:55         ` Michal Hocko
  0 siblings, 1 reply; 25+ messages in thread
From: Arun KS @ 2018-10-11  2:29 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Vlastimil Babka, kys, haiyangz, sthemmin, boris.ostrovsky,
	jgross, akpm, dan.j.williams, iamjoonsoo.kim, gregkh, osalvador,
	malat, kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman,
	aaron.lu, devel, linux-kernel, linux-mm, xen-devel, vatsa,
	vinmenon, getarunks

On 2018-10-10 23:03, Michal Hocko wrote:
> On Wed 10-10-18 22:26:41, Arun KS wrote:
>> On 2018-10-10 21:00, Vlastimil Babka wrote:
>> > On 10/5/18 10:10 AM, Arun KS wrote:
>> > > 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 <arunks@codeaurora.org>
>> >
>> > [...]
>> >
>> > > @@ -655,26 +655,44 @@ 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)
>> > >  {
>> > > -	__online_page_set_limits(page);
>> >
>> > This is now not called anymore, although the xen/hv variants still do
>> > it. The function seems empty these days, maybe remove it as a followup
>> > cleanup?
>> >
>> > > -	__online_page_increment_counters(page);
>> > > -	__online_page_free(page);
>> > > +	__free_pages_core(page, order);
>> > > +	totalram_pages += (1UL << order);
>> > > +#ifdef CONFIG_HIGHMEM
>> > > +	if (PageHighMem(page))
>> > > +		totalhigh_pages += (1UL << order);
>> > > +#endif
>> >
>> > __online_page_increment_counters() would have used
>> > adjust_managed_page_count() which would do the changes under
>> > managed_page_count_lock. Are we safe without the lock? If yes, there
>> > should perhaps be a comment explaining why.
>> 
>> Looks unsafe without managed_page_count_lock.
> 
> Why does it matter actually? We cannot online/offline memory in
> parallel. This is not the case for the boot where we initialize memory
> in parallel on multiple nodes. So this seems to be safe currently 
> unless
> I am missing something. A comment explaining that would be helpful
> though.

Other main callers of adjust_manage_page_count(),

static inline void free_reserved_page(struct page *page)
{
         __free_reserved_page(page);
         adjust_managed_page_count(page, 1);
}

static inline void mark_page_reserved(struct page *page)
{
         SetPageReserved(page);
         adjust_managed_page_count(page, -1);
}

Won't they race with memory hotplug?

Few more,
./drivers/xen/balloon.c:519:            adjust_managed_page_count(page, 
-1);
./drivers/virtio/virtio_balloon.c:175:  adjust_managed_page_count(page, 
-1);
./drivers/virtio/virtio_balloon.c:196:  adjust_managed_page_count(page, 
1);
./mm/hugetlb.c:2158:                    adjust_managed_page_count(page, 
1 << h->order);

Regards,
Arun

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-11  2:29       ` Arun KS
@ 2018-10-11  7:55         ` Michal Hocko
  2018-10-19  2:18           ` Andrew Morton
  0 siblings, 1 reply; 25+ messages in thread
From: Michal Hocko @ 2018-10-11  7:55 UTC (permalink / raw)
  To: Arun KS
  Cc: Vlastimil Babka, kys, haiyangz, sthemmin, boris.ostrovsky,
	jgross, akpm, dan.j.williams, iamjoonsoo.kim, gregkh, osalvador,
	malat, kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman,
	aaron.lu, devel, linux-kernel, linux-mm, xen-devel, vatsa,
	vinmenon, getarunks

On Thu 11-10-18 07:59:32, Arun KS wrote:
> On 2018-10-10 23:03, Michal Hocko wrote:
> > On Wed 10-10-18 22:26:41, Arun KS wrote:
> > > On 2018-10-10 21:00, Vlastimil Babka wrote:
> > > > On 10/5/18 10:10 AM, Arun KS wrote:
> > > > > 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 <arunks@codeaurora.org>
> > > >
> > > > [...]
> > > >
> > > > > @@ -655,26 +655,44 @@ 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)
> > > > >  {
> > > > > -	__online_page_set_limits(page);
> > > >
> > > > This is now not called anymore, although the xen/hv variants still do
> > > > it. The function seems empty these days, maybe remove it as a followup
> > > > cleanup?
> > > >
> > > > > -	__online_page_increment_counters(page);
> > > > > -	__online_page_free(page);
> > > > > +	__free_pages_core(page, order);
> > > > > +	totalram_pages += (1UL << order);
> > > > > +#ifdef CONFIG_HIGHMEM
> > > > > +	if (PageHighMem(page))
> > > > > +		totalhigh_pages += (1UL << order);
> > > > > +#endif
> > > >
> > > > __online_page_increment_counters() would have used
> > > > adjust_managed_page_count() which would do the changes under
> > > > managed_page_count_lock. Are we safe without the lock? If yes, there
> > > > should perhaps be a comment explaining why.
> > > 
> > > Looks unsafe without managed_page_count_lock.
> > 
> > Why does it matter actually? We cannot online/offline memory in
> > parallel. This is not the case for the boot where we initialize memory
> > in parallel on multiple nodes. So this seems to be safe currently unless
> > I am missing something. A comment explaining that would be helpful
> > though.
> 
> Other main callers of adjust_manage_page_count(),
> 
> static inline void free_reserved_page(struct page *page)
> {
>         __free_reserved_page(page);
>         adjust_managed_page_count(page, 1);
> }
> 
> static inline void mark_page_reserved(struct page *page)
> {
>         SetPageReserved(page);
>         adjust_managed_page_count(page, -1);
> }
> 
> Won't they race with memory hotplug?
> 
> Few more,
> ./drivers/xen/balloon.c:519:            adjust_managed_page_count(page, -1);
> ./drivers/virtio/virtio_balloon.c:175:  adjust_managed_page_count(page, -1);
> ./drivers/virtio/virtio_balloon.c:196:  adjust_managed_page_count(page, 1);
> ./mm/hugetlb.c:2158:                    adjust_managed_page_count(page, 1 <<
> h->order);

They can, and I have missed those.

-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-10 16:56   ` Arun KS
  2018-10-10 17:33     ` Michal Hocko
@ 2018-10-11  8:07     ` Vlastimil Babka
  2018-10-11  8:15       ` Michal Hocko
  2018-11-19 22:15       ` Wei Yang
  1 sibling, 2 replies; 25+ messages in thread
From: Vlastimil Babka @ 2018-10-11  8:07 UTC (permalink / raw)
  To: Arun KS
  Cc: kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, mhocko, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On 10/10/18 6:56 PM, Arun KS wrote:
> On 2018-10-10 21:00, Vlastimil Babka wrote:
>> On 10/5/18 10:10 AM, Arun KS wrote:
>>> 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 <arunks@codeaurora.org>
>>
>> [...]
>>
>>> @@ -655,26 +655,44 @@ 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)
>>>  {
>>> -	__online_page_set_limits(page);
>>
>> This is now not called anymore, although the xen/hv variants still do
>> it. The function seems empty these days, maybe remove it as a followup
>> cleanup?
>>
>>> -	__online_page_increment_counters(page);
>>> -	__online_page_free(page);
>>> +	__free_pages_core(page, order);
>>> +	totalram_pages += (1UL << order);
>>> +#ifdef CONFIG_HIGHMEM
>>> +	if (PageHighMem(page))
>>> +		totalhigh_pages += (1UL << order);
>>> +#endif
>>
>> __online_page_increment_counters() would have used
>> adjust_managed_page_count() which would do the changes under
>> managed_page_count_lock. Are we safe without the lock? If yes, there
>> should perhaps be a comment explaining why.
> 
> Looks unsafe without managed_page_count_lock. I think better have a 
> similar implementation of free_boot_core() in memory_hotplug.c like we 
> had in version 1 of patch. And use adjust_managed_page_count() instead 
> of page_zone(page)->managed_pages += nr_pages;
> 
> https://lore.kernel.org/patchwork/patch/989445/

Looks like deferred_free_range() has the same problem calling
__free_pages_core() to adjust zone->managed_pages. I expect
__free_pages_bootmem() is OK because at that point the system is still
single-threaded?
Could be solved by moving that out of __free_pages_core().

But do we care about readers potentially seeing a store tear? If yes
then maybe these counters should be converted to atomics...

> -static void generic_online_page(struct page *page)
> +static int generic_online_page(struct page *page, unsigned int order)
>   {
> -	__online_page_set_limits(page);
> -	__online_page_increment_counters(page);
> -	__online_page_free(page);
> +	unsigned long nr_pages = 1 << order;
> +	struct page *p = page;
> +
> +	for (loop = 0 ; loop < nr_pages ; loop++, p++) {
> +		__ClearPageReserved(p);
> +		set_page_count(p, 0);
> +	}
> +
> +	adjust_managed_page_count(page, nr_pages);
> +	set_page_refcounted(page);
> +	__free_pages(page, order);
> +
> +	return 0;
> +}
> 
> 
> Regards,
> Arun
> 

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-11  8:07     ` Vlastimil Babka
@ 2018-10-11  8:15       ` Michal Hocko
  2018-11-19 22:15       ` Wei Yang
  1 sibling, 0 replies; 25+ messages in thread
From: Michal Hocko @ 2018-10-11  8:15 UTC (permalink / raw)
  To: Vlastimil Babka
  Cc: Arun KS, kys, haiyangz, sthemmin, boris.ostrovsky, jgross, akpm,
	dan.j.williams, iamjoonsoo.kim, gregkh, osalvador, malat,
	kirill.shutemov, jrdr.linux, yasu.isimatu, mgorman, aaron.lu,
	devel, linux-kernel, linux-mm, xen-devel, vatsa, vinmenon,
	getarunks

On Thu 11-10-18 10:07:02, Vlastimil Babka wrote:
> On 10/10/18 6:56 PM, Arun KS wrote:
> > On 2018-10-10 21:00, Vlastimil Babka wrote:
> >> On 10/5/18 10:10 AM, Arun KS wrote:
> >>> 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 <arunks@codeaurora.org>
> >>
> >> [...]
> >>
> >>> @@ -655,26 +655,44 @@ 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)
> >>>  {
> >>> -	__online_page_set_limits(page);
> >>
> >> This is now not called anymore, although the xen/hv variants still do
> >> it. The function seems empty these days, maybe remove it as a followup
> >> cleanup?
> >>
> >>> -	__online_page_increment_counters(page);
> >>> -	__online_page_free(page);
> >>> +	__free_pages_core(page, order);
> >>> +	totalram_pages += (1UL << order);
> >>> +#ifdef CONFIG_HIGHMEM
> >>> +	if (PageHighMem(page))
> >>> +		totalhigh_pages += (1UL << order);
> >>> +#endif
> >>
> >> __online_page_increment_counters() would have used
> >> adjust_managed_page_count() which would do the changes under
> >> managed_page_count_lock. Are we safe without the lock? If yes, there
> >> should perhaps be a comment explaining why.
> > 
> > Looks unsafe without managed_page_count_lock. I think better have a 
> > similar implementation of free_boot_core() in memory_hotplug.c like we 
> > had in version 1 of patch. And use adjust_managed_page_count() instead 
> > of page_zone(page)->managed_pages += nr_pages;
> > 
> > https://lore.kernel.org/patchwork/patch/989445/
> 
> Looks like deferred_free_range() has the same problem calling
> __free_pages_core() to adjust zone->managed_pages.

deferred initialization has one thread per node AFAIR so we cannot race
on managed_pages updates. Well, unless some of the mentioned can run
that early which I dunno.

> __free_pages_bootmem() is OK because at that point the system is still
> single-threaded?
> Could be solved by moving that out of __free_pages_core().
> 
> But do we care about readers potentially seeing a store tear? If yes
> then maybe these counters should be converted to atomics...

I wanted to suggest that already but I have no idea whether the lock
instructions would cause more overhead.
-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-11  7:55         ` Michal Hocko
@ 2018-10-19  2:18           ` Andrew Morton
  2018-10-19  8:07             ` Michal Hocko
  0 siblings, 1 reply; 25+ messages in thread
From: Andrew Morton @ 2018-10-19  2:18 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Arun KS, Vlastimil Babka, kys, haiyangz, sthemmin,
	boris.ostrovsky, jgross, dan.j.williams, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On Thu, 11 Oct 2018 09:55:03 +0200 Michal Hocko <mhocko@kernel.org> wrote:

> > > > > This is now not called anymore, although the xen/hv variants still do
> > > > > it. The function seems empty these days, maybe remove it as a followup
> > > > > cleanup?
> > > > >
> > > > > > -	__online_page_increment_counters(page);
> > > > > > -	__online_page_free(page);
> > > > > > +	__free_pages_core(page, order);
> > > > > > +	totalram_pages += (1UL << order);
> > > > > > +#ifdef CONFIG_HIGHMEM
> > > > > > +	if (PageHighMem(page))
> > > > > > +		totalhigh_pages += (1UL << order);
> > > > > > +#endif
> > > > >
> > > > > __online_page_increment_counters() would have used
> > > > > adjust_managed_page_count() which would do the changes under
> > > > > managed_page_count_lock. Are we safe without the lock? If yes, there
> > > > > should perhaps be a comment explaining why.
> > > > 
> > > > Looks unsafe without managed_page_count_lock.
> > > 
> > > Why does it matter actually? We cannot online/offline memory in
> > > parallel. This is not the case for the boot where we initialize memory
> > > in parallel on multiple nodes. So this seems to be safe currently unless
> > > I am missing something. A comment explaining that would be helpful
> > > though.
> > 
> > Other main callers of adjust_manage_page_count(),
> > 
> > static inline void free_reserved_page(struct page *page)
> > {
> >         __free_reserved_page(page);
> >         adjust_managed_page_count(page, 1);
> > }
> > 
> > static inline void mark_page_reserved(struct page *page)
> > {
> >         SetPageReserved(page);
> >         adjust_managed_page_count(page, -1);
> > }
> > 
> > Won't they race with memory hotplug?
> > 
> > Few more,
> > ./drivers/xen/balloon.c:519:            adjust_managed_page_count(page, -1);
> > ./drivers/virtio/virtio_balloon.c:175:  adjust_managed_page_count(page, -1);
> > ./drivers/virtio/virtio_balloon.c:196:  adjust_managed_page_count(page, 1);
> > ./mm/hugetlb.c:2158:                    adjust_managed_page_count(page, 1 <<
> > h->order);
> 
> They can, and I have missed those.

So this patch needs more work, yes?

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-19  2:18           ` Andrew Morton
@ 2018-10-19  8:07             ` Michal Hocko
  2018-10-22 10:33               ` Arun KS
  0 siblings, 1 reply; 25+ messages in thread
From: Michal Hocko @ 2018-10-19  8:07 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Arun KS, Vlastimil Babka, kys, haiyangz, sthemmin,
	boris.ostrovsky, jgross, dan.j.williams, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On Thu 18-10-18 19:18:25, Andrew Morton wrote:
[...]
> So this patch needs more work, yes?

Yes, I've talked to Arun (he is offline until next week) offlist and he
will play with this some more.

-- 
Michal Hocko
SUSE Labs

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-19  8:07             ` Michal Hocko
@ 2018-10-22 10:33               ` Arun KS
  2018-11-05  9:42                 ` Arun KS
  0 siblings, 1 reply; 25+ messages in thread
From: Arun KS @ 2018-10-22 10:33 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Andrew Morton, Vlastimil Babka, kys, haiyangz, sthemmin,
	boris.ostrovsky, jgross, dan.j.williams, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On 2018-10-19 13:37, Michal Hocko wrote:
> On Thu 18-10-18 19:18:25, Andrew Morton wrote:
> [...]
>> So this patch needs more work, yes?
> 
> Yes, I've talked to Arun (he is offline until next week) offlist and he
> will play with this some more.

Converted totalhigh_pages, totalram_pages and zone->managed_page to 
atomic and tested hot add. Latency is not effected with this change.
Will send out a separate patch on top of this one.

Regards,
Arun

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-22 10:33               ` Arun KS
@ 2018-11-05  9:42                 ` Arun KS
  2018-11-05 21:44                   ` Andrew Morton
  0 siblings, 1 reply; 25+ messages in thread
From: Arun KS @ 2018-11-05  9:42 UTC (permalink / raw)
  To: Michal Hocko
  Cc: Andrew Morton, Vlastimil Babka, kys, haiyangz, sthemmin,
	boris.ostrovsky, jgross, dan.j.williams, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On 2018-10-22 16:03, Arun KS wrote:
> On 2018-10-19 13:37, Michal Hocko wrote:
>> On Thu 18-10-18 19:18:25, Andrew Morton wrote:
>> [...]
>>> So this patch needs more work, yes?
>> 
>> Yes, I've talked to Arun (he is offline until next week) offlist and 
>> he
>> will play with this some more.
> 
> Converted totalhigh_pages, totalram_pages and zone->managed_page to
> atomic and tested hot add. Latency is not effected with this change.
> Will send out a separate patch on top of this one.
Hello Andrew/Michal,

Will this be going in subsequent -rcs?

Regards,
Arun

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-11-05  9:42                 ` Arun KS
@ 2018-11-05 21:44                   ` Andrew Morton
  2018-11-06  5:31                     ` Arun KS
  0 siblings, 1 reply; 25+ messages in thread
From: Andrew Morton @ 2018-11-05 21:44 UTC (permalink / raw)
  To: Arun KS
  Cc: Michal Hocko, Vlastimil Babka, kys, haiyangz, sthemmin,
	boris.ostrovsky, jgross, dan.j.williams, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On Mon, 05 Nov 2018 15:12:27 +0530 Arun KS <arunks@codeaurora.org> wrote:

> On 2018-10-22 16:03, Arun KS wrote:
> > On 2018-10-19 13:37, Michal Hocko wrote:
> >> On Thu 18-10-18 19:18:25, Andrew Morton wrote:
> >> [...]
> >>> So this patch needs more work, yes?
> >> 
> >> Yes, I've talked to Arun (he is offline until next week) offlist and 
> >> he
> >> will play with this some more.
> > 
> > Converted totalhigh_pages, totalram_pages and zone->managed_page to
> > atomic and tested hot add. Latency is not effected with this change.
> > Will send out a separate patch on top of this one.
> Hello Andrew/Michal,
> 
> Will this be going in subsequent -rcs?

I thought were awaiting a new version?  "Will send out a separate patch
on top of this one"?

I do think a resend would be useful, please.  Ensure the changelog is
updated to capture the above info and any other worthy issues which
arose during review.

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-11-05 21:44                   ` Andrew Morton
@ 2018-11-06  5:31                     ` Arun KS
  0 siblings, 0 replies; 25+ messages in thread
From: Arun KS @ 2018-11-06  5:31 UTC (permalink / raw)
  To: Andrew Morton
  Cc: Michal Hocko, Vlastimil Babka, kys, haiyangz, sthemmin,
	boris.ostrovsky, jgross, dan.j.williams, iamjoonsoo.kim, gregkh,
	osalvador, malat, kirill.shutemov, jrdr.linux, yasu.isimatu,
	mgorman, aaron.lu, devel, linux-kernel, linux-mm, xen-devel,
	vatsa, vinmenon, getarunks

On 2018-11-06 03:14, Andrew Morton wrote:
> On Mon, 05 Nov 2018 15:12:27 +0530 Arun KS <arunks@codeaurora.org> 
> wrote:
> 
>> On 2018-10-22 16:03, Arun KS wrote:
>> > On 2018-10-19 13:37, Michal Hocko wrote:
>> >> On Thu 18-10-18 19:18:25, Andrew Morton wrote:
>> >> [...]
>> >>> So this patch needs more work, yes?
>> >>
>> >> Yes, I've talked to Arun (he is offline until next week) offlist and
>> >> he
>> >> will play with this some more.
>> >
>> > Converted totalhigh_pages, totalram_pages and zone->managed_page to
>> > atomic and tested hot add. Latency is not effected with this change.
>> > Will send out a separate patch on top of this one.
>> Hello Andrew/Michal,
>> 
>> Will this be going in subsequent -rcs?
> 
> I thought were awaiting a new version?  "Will send out a separate patch
> on top of this one"?

Sorry for confusion. I sent out an incremental patch converting counters 
to atomics.

https://patchwork.kernel.org/cover/10657217/


> 
> I do think a resend would be useful, please.  Ensure the changelog is
> updated to capture the above info and any other worthy issues which
> arose during review.

Will do that.

Regards,
Arun

^ permalink raw reply	[flat|nested] 25+ messages in thread

* Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
  2018-10-11  8:07     ` Vlastimil Babka
  2018-10-11  8:15       ` Michal Hocko
@ 2018-11-19 22:15       ` Wei Yang
  1 sibling, 0 replies; 25+ messages in thread
From: Wei Yang @ 2018-11-19 22:15 UTC (permalink / raw)
  To: Vlastimil Babka
  Cc: arunks, K. Y. Srinivasan, Haiyang Zhang, Stephen Hemminger,
	Boris Ostrovsky, jgross, Andrew Morton, Dan Williams,
	Michal Hocko, iamjoonsoo.kim, Greg Kroah-Hartman, Oscar Salvador,
	Mathieu Malaterre, Kirill A . Shutemov, jrdr.linux,
	Yasuaki Ishimatsu, Mel Gorman, aaron.lu, devel,
	Linux Kernel Mailing List, Linux-MM, xen-devel, vatsa,
	Vinayak Menon, getarunks

On Thu, Oct 11, 2018 at 6:05 PM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 10/10/18 6:56 PM, Arun KS wrote:
> > On 2018-10-10 21:00, Vlastimil Babka wrote:
> >> On 10/5/18 10:10 AM, Arun KS wrote:
> >>> 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 <arunks@codeaurora.org>
> >>
> >> [...]
> >>
> >>> @@ -655,26 +655,44 @@ 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)
> >>>  {
> >>> -   __online_page_set_limits(page);
> >>
> >> This is now not called anymore, although the xen/hv variants still do
> >> it. The function seems empty these days, maybe remove it as a followup
> >> cleanup?
> >>
> >>> -   __online_page_increment_counters(page);
> >>> -   __online_page_free(page);
> >>> +   __free_pages_core(page, order);
> >>> +   totalram_pages += (1UL << order);
> >>> +#ifdef CONFIG_HIGHMEM
> >>> +   if (PageHighMem(page))
> >>> +           totalhigh_pages += (1UL << order);
> >>> +#endif
> >>
> >> __online_page_increment_counters() would have used
> >> adjust_managed_page_count() which would do the changes under
> >> managed_page_count_lock. Are we safe without the lock? If yes, there
> >> should perhaps be a comment explaining why.
> >
> > Looks unsafe without managed_page_count_lock. I think better have a
> > similar implementation of free_boot_core() in memory_hotplug.c like we
> > had in version 1 of patch. And use adjust_managed_page_count() instead
> > of page_zone(page)->managed_pages += nr_pages;
> >
> > https://lore.kernel.org/patchwork/patch/989445/
>
> Looks like deferred_free_range() has the same problem calling
> __free_pages_core() to adjust zone->managed_pages. I expect
> __free_pages_bootmem() is OK because at that point the system is still
> single-threaded?
> Could be solved by moving that out of __free_pages_core().
>

Seems deferred_free_range() is protected by
pgdat_resize_lock()/pgdat_resize_unlock().

Which protects pgdat's zones, if I am right.

> But do we care about readers potentially seeing a store tear? If yes
> then maybe these counters should be converted to atomics...
>
> > -static void generic_online_page(struct page *page)
> > +static int generic_online_page(struct page *page, unsigned int order)
> >   {
> > -     __online_page_set_limits(page);
> > -     __online_page_increment_counters(page);
> > -     __online_page_free(page);
> > +     unsigned long nr_pages = 1 << order;
> > +     struct page *p = page;
> > +
> > +     for (loop = 0 ; loop < nr_pages ; loop++, p++) {
> > +             __ClearPageReserved(p);
> > +             set_page_count(p, 0);
> > +     }
> > +
> > +     adjust_managed_page_count(page, nr_pages);
> > +     set_page_refcounted(page);
> > +     __free_pages(page, order);
> > +
> > +     return 0;
> > +}
> >
> >
> > Regards,
> > Arun
> >
>

^ permalink raw reply	[flat|nested] 25+ messages in thread

end of thread, back to index

Thread overview: 25+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-10-05  8:10 [PATCH v5 1/2] memory_hotplug: Free pages as higher order Arun KS
2018-10-05  8:10 ` [PATCH v5 2/2] mm/page_alloc: remove software prefetching in __free_pages_core Arun KS
2018-10-09  9:30   ` Michal Hocko
2018-10-10 16:36   ` Vlastimil Babka
2018-10-08  7:34 ` [PATCH v5 1/2] memory_hotplug: Free pages as higher order Oscar Salvador
2018-10-09  9:29 ` Michal Hocko
2018-10-09  9:54   ` Arun KS
2018-10-09 11:06     ` Michal Hocko
2018-10-10  8:07 ` Oscar Salvador
2018-10-10 10:51   ` Arun KS
2018-10-10 11:01     ` Oscar Salvador
2018-10-10 15:30 ` Vlastimil Babka
2018-10-10 16:56   ` Arun KS
2018-10-10 17:33     ` Michal Hocko
2018-10-11  2:29       ` Arun KS
2018-10-11  7:55         ` Michal Hocko
2018-10-19  2:18           ` Andrew Morton
2018-10-19  8:07             ` Michal Hocko
2018-10-22 10:33               ` Arun KS
2018-11-05  9:42                 ` Arun KS
2018-11-05 21:44                   ` Andrew Morton
2018-11-06  5:31                     ` Arun KS
2018-10-11  8:07     ` Vlastimil Babka
2018-10-11  8:15       ` Michal Hocko
2018-11-19 22:15       ` Wei Yang

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