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Date: Mon, 24 Sep 2018 13:27:22 +0530
From: Arun KS <arunks@...eaurora.org>
To: Dan Williams <dan.j.williams@...el.com>
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Juergen Gross <jgross@...e.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Michal Hocko <mhocko@...e.com>,
Vlastimil Babka <vbabka@...e.cz>,
Pavel Tatashin <pasha.tatashin@...cle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>, osalvador@...e.de,
malat@...ian.org, Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
devel@...uxdriverproject.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux MM <linux-mm@...ck.org>,
xen-devel <xen-devel@...ts.xenproject.org>, vatsa@...eaurora.org,
vinmenon@...eaurora.org, getarunks@...il.com
Subject: Re: [PATCH] memory_hotplug: Free pages as higher order
On 2018-09-21 21:12, Dan Williams wrote:
> On Fri, Sep 21, 2018 at 2:40 AM Arun KS <arunks@...eaurora.org> 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@...eaurora.org>
>>
>> ---
>>
>> 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(-)
>>
>> 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..010cf4d 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);
>> @@ -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);
>>
>> 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/memory_hotplug.c b/mm/memory_hotplug.c
>> index 38d94b7..24c2b8e 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 +655,57 @@ 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)
>> {
>> - __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.
Hello Dan,
Thanks for your comment. I tested on arm64 with and without prefetch and
as you guessed, the one without prefetch is slightly better.
Will remove prefetch before sending next version.
Regards,
Arun
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