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From: Arun KS <arunks@codeaurora.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	kys@microsoft.com, haiyangz@microsoft.com,
	sthemmin@microsoft.com, boris.ostrovsky@oracle.com,
	jgross@suse.com, akpm@linux-foundation.org,
	dan.j.williams@intel.com, iamjoonsoo.kim@lge.com,
	gregkh@linuxfoundation.org, osalvador@suse.de, malat@debian.org,
	kirill.shutemov@linux.intel.com, jrdr.linux@gmail.com,
	yasu.isimatu@gmail.com, mgorman@techsingularity.net,
	aaron.lu@intel.com, devel@linuxdriverproject.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	xen-devel@lists.xenproject.org, vatsa@codeaurora.org,
	vinmenon@codeaurora.org, getarunks@gmail.com
Subject: Re: [PATCH v5 1/2] memory_hotplug: Free pages as higher order
Date: Thu, 11 Oct 2018 07:59:32 +0530	[thread overview]
Message-ID: <a2d576a5fc82cdf54fc89409686e58f5@codeaurora.org> (raw)
In-Reply-To: <20181010173334.GL5873@dhcp22.suse.cz>

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

  reply	other threads:[~2018-10-11  2:29 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
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 [this message]
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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