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From: Michal Hocko <mhocko@kernel.org>
To: Arun KS <arunks@codeaurora.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: Wed, 10 Oct 2018 19:33:34 +0200	[thread overview]
Message-ID: <20181010173334.GL5873@dhcp22.suse.cz> (raw)
In-Reply-To: <efb65160af41d0e18cb2dcb30c2fb86a@codeaurora.org>

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

  reply	other threads:[~2018-10-10 17:33 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 [this message]
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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