Re: [PATCH v9] mm/page_alloc.c: memory_hotplug: free pages as higher order

[Arun KS <arunks@codeaurora.org>]

On 2019-01-10 21:53, Alexander Duyck wrote:
> On Thu, 2019-01-10 at 11:05 +0530, Arun KS wrote:
>> When freeing pages are done with higher order, time spent 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 times.  Modify
>> external providers of online callback to align with the change.
>> 
>> Signed-off-by: Arun KS <arunks@codeaurora.org>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> 
> So I decided to give this one last thorough review and I think I might
> have found a few more minor issues, but not anything that is
> necessarily a showstopper.
> 
> Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> 
>> ---
>> Changes since v8:
>> - Remove return type change for online_page_callback.
>> - Use consistent names for external online_page providers.
>> - Fix onlined_pages accounting.
>> 
>> Changes since v7:
>> - Rebased to 5.0-rc1.
>> - Fixed onlined_pages accounting.
>> - Added comment for return value of online_page_callback.
>> - Renamed xen_bring_pgs_online to xen_online_pages.
>> 
>> Changes since v6:
>> - Rebased to 4.20
>> - Changelog updated.
>> - No improvement seen on arm64, hence removed removal of prefetch.
>> 
>> Changes since v5:
>> - Rebased to 4.20-rc1.
>> - Changelog updated.
>> 
>> 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.
>> 
>> v8: https://lore.kernel.org/patchwork/patch/1030332/
>> v7: https://lore.kernel.org/patchwork/patch/1028908/
>> v6: https://lore.kernel.org/patchwork/patch/1007253/
>> v5: https://lore.kernel.org/patchwork/patch/995739/
>> 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        |  4 ++--
>>  drivers/xen/balloon.c          | 15 ++++++++++-----
>>  include/linux/memory_hotplug.h |  2 +-
>>  mm/internal.h                  |  1 +
>>  mm/memory_hotplug.c            | 37 
>> +++++++++++++++++++++++++------------
>>  mm/page_alloc.c                |  8 ++++----
>>  6 files changed, 43 insertions(+), 24 deletions(-)
>> 
>> diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
>> index 5301fef..55d79f8 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 void hv_online_page(struct page *pg, unsigned int order)
>>  {
>>  	struct hv_hotadd_state *has;
>>  	unsigned long flags;
>> @@ -783,7 +783,7 @@ static void hv_online_page(struct page *pg)
>>  		if ((pfn < has->start_pfn) || (pfn >= has->end_pfn))
>>  			continue;
>> 
> 
> I haven't followed earlier reviews, but do we know for certain the
> entire range being onlined will fit within a single hv_hotadd_state? If
> nothing else it seems like this check should be updated so that we are
> checking to verify that pfn + (1UL << order) is less than or equal to
> has->end_pfn.

Good catch. I ll change the check to,
          if ((pfn < has->start_pfn) ||
                   (pfn + (1UL << order) >= 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);
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index ceb5048..d107447 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -369,14 +369,19 @@ static enum bp_state 
>> reserve_additional_memory(void)
>>  	return BP_ECANCELED;
>>  }
>> 
>> -static void xen_online_page(struct page *page)
>> +static void xen_online_page(struct page *page, unsigned int order)
>>  {
>> -	__online_page_set_limits(page);
>> +	unsigned long i, size = (1 << order);
>> +	unsigned long start_pfn = page_to_pfn(page);
>> +	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);
>>  }
>> 
>> diff --git a/include/linux/memory_hotplug.h 
>> b/include/linux/memory_hotplug.h
>> index 07da5c6..e368730 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 void (*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 f4a7bb0..536bc2a 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 memblock_free_pages(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 b9a667d..77dff24 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 void 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);
>> @@ -656,26 +656,39 @@ void __online_page_free(struct page *page)
>>  }
>>  EXPORT_SYMBOL_GPL(__online_page_free);
>> 
>> -static void generic_online_page(struct page *page)
>> +static void 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_add(1UL << order);
>> +#ifdef CONFIG_HIGHMEM
>> +	if (PageHighMem(page))
>> +		totalhigh_pages_add(1UL << order);
>> +#endif
>> +}
>> +
>> +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)));
> 
> So this is mostly just optimization related so you can ignore this
> suggestion if you want. I was looking at this and it occurred to me
> that I don't think you need to convert this to a physical address do
> you?
> 
> Couldn't you just do something like the following:
> 		if ((end - start) >= (1UL << (MAX_ORDER - 1))
> 			order = MAX_ORDER - 1;
> 		else
> 			order = __fls(end - start);
> 
> I would think this would save you a few steps in terms of conversions
> and such since you are already working in page frame numbers anyway so
> a block of 8 pfns would represent an order 3 page wouldn't it?
> 
> Also it seems like an alternative to using "end" would be to just track
> nr_pages. Then you wouldn't have to do the "end - start" math in a few
> spots as long as you remembered to decrement nr_pages by the amount you
> increment start by.

Thanks for that. How about this?

static int online_pages_blocks(unsigned long start, unsigned long 
nr_pages)
{
         unsigned long end = start + nr_pages;
         int order;

         while (nr_pages) {
                 if (nr_pages >= (1UL << (MAX_ORDER - 1)))
                         order = MAX_ORDER - 1;
                 else
                         order = __fls(nr_pages);

                 (*online_page_callback)(pfn_to_page(start), order);
                 nr_pages -= (1UL << order);
                 start += (1UL << order);
         }
         return end - start;
}

Regards,
Arun

> 
>> +		(*online_page_callback)(pfn_to_page(start), order);
>> +
>> +		onlined_pages += (1UL << order);
>> +		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 d295c9b..883212a 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -1303,7 +1303,7 @@ 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;
>> @@ -1382,7 +1382,7 @@ void __init memblock_free_pages(struct page 
>> *page, unsigned long pfn,
>>  {
>>  	if (early_page_uninitialised(pfn))
>>  		return;
>> -	return __free_pages_boot_core(page, order);
>> +	__free_pages_core(page, order);
>>  }
>> 
>>  /*
>> @@ -1472,14 +1472,14 @@ 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);
>>  	}
>>  }
>>