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From: Mel Gorman <mgorman@techsingularity.net>
To: David Hildenbrand <david@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Hillf Danton <hdanton@sina.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Michal Hocko <mhocko@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>, "Tang, Feng" <feng.tang@intel.com>
Subject: Re: [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs
Date: Fri, 28 May 2021 10:49:49 +0100	[thread overview]
Message-ID: <20210528094949.GL30378@techsingularity.net> (raw)
In-Reply-To: <e73d39cc-df2f-5000-0212-6073955fb291@redhat.com>

On Fri, May 28, 2021 at 11:08:01AM +0200, David Hildenbrand wrote:
> On 28.05.21 11:03, David Hildenbrand wrote:
> > On 28.05.21 10:55, Mel Gorman wrote:
> > > On Thu, May 27, 2021 at 12:36:21PM -0700, Dave Hansen wrote:
> > > > Hi Mel,
> > > > 
> > > > Feng Tang tossed these on a "Cascade Lake" system with 96 threads and
> > > > ~512G of persistent memory and 128G of DRAM.  The PMEM is in "volatile
> > > > use" mode and being managed via the buddy just like the normal RAM.
> > > > 
> > > > The PMEM zones are big ones:
> > > > 
> > > >           present  65011712 = 248 G
> > > >           high       134595 = 525 M
> > > > 
> > > > The PMEM nodes, of course, don't have any CPUs in them.
> > > > 
> > > > With your series, the pcp->high value per-cpu is 69584 pages or about
> > > > 270MB per CPU.  Scaled up by the 96 CPU threads, that's ~26GB of
> > > > worst-case memory in the pcps per zone, or roughly 10% of the size of
> > > > the zone.
> > 
> > When I read about having such big amounts of free memory theoretically
> > stuck in PCP lists, I guess we really want to start draining the PCP in
> > alloc_contig_range(), just as we do with memory hotunplug when offlining.
> > 
> 
> Correction: we already drain the pcp, we just don't temporarily disable it,
> so a race as described in offline_pages() could apply:
> 
> "Disable pcplists so that page isolation cannot race with freeing
>  in a way that pages from isolated pageblock are left on pcplists."
> 
> Guess we'd then want to move the draining before start_isolate_page_range()
> in alloc_contig_range().
> 

Or instead of draining, validate the PFN range in alloc_contig_range
is within the same zone and if so, call zone_pcp_disable() before
start_isolate_page_range and enable after __alloc_contig_migrate_range.

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2021-05-28  9:49 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-25  8:01 Mel Gorman
2021-05-25  8:01 ` [PATCH 1/6] mm/page_alloc: Delete vm.percpu_pagelist_fraction Mel Gorman
2021-05-26 17:41   ` Vlastimil Babka
2021-05-25  8:01 ` [PATCH 2/6] mm/page_alloc: Disassociate the pcp->high from pcp->batch Mel Gorman
2021-05-26 18:14   ` Vlastimil Babka
2021-05-27 10:52     ` Mel Gorman
2021-05-28 10:27       ` Vlastimil Babka
2021-05-25  8:01 ` [PATCH 3/6] mm/page_alloc: Adjust pcp->high after CPU hotplug events Mel Gorman
2021-05-28 11:08   ` Vlastimil Babka
2021-05-25  8:01 ` [PATCH 4/6] mm/page_alloc: Scale the number of pages that are batch freed Mel Gorman
2021-05-28 11:19   ` Vlastimil Babka
2021-05-25  8:01 ` [PATCH 5/6] mm/page_alloc: Limit the number of pages on PCP lists when reclaim is active Mel Gorman
2021-05-28 11:43   ` Vlastimil Babka
2021-05-25  8:01 ` [PATCH 6/6] mm/page_alloc: Introduce vm.percpu_pagelist_high_fraction Mel Gorman
2021-05-28 11:59   ` Vlastimil Babka
2021-05-28 12:53     ` Mel Gorman
2021-05-28 14:38       ` Vlastimil Babka
2021-05-27 19:36 ` [PATCH 0/6 v2] Calculate pcp->high based on zone sizes and active CPUs Dave Hansen
2021-05-28  8:55   ` Mel Gorman
2021-05-28  9:03     ` David Hildenbrand
2021-05-28  9:08       ` David Hildenbrand
2021-05-28  9:49         ` Mel Gorman [this message]
2021-05-28  9:52           ` David Hildenbrand
2021-05-28 10:09             ` Mel Gorman
2021-05-28 10:21               ` David Hildenbrand
2021-05-28 12:12     ` Vlastimil Babka
2021-05-28 12:37       ` Mel Gorman
2021-05-28 14:39     ` Dave Hansen
2021-05-28 15:18       ` Mel Gorman
2021-05-28 16:17         ` Dave Hansen
2021-05-31 12:00           ` Feng Tang

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