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From: Vlastimil Babka <vbabka@suse.cz>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Linux-MM <linux-mm@kvack.org>,
	Linux-RT-Users <linux-rt-users@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Chuck Lever <chuck.lever@oracle.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Matthew Wilcox <willy@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@kernel.org>,
	Oscar Salvador <osalvador@suse.de>
Subject: Re: [PATCH 04/11] mm/vmstat: Convert NUMA statistics to basic NUMA counters
Date: Wed, 14 Apr 2021 17:56:53 +0200
Message-ID: <c4dff8a5-7959-c191-c66d-23a515244b80@suse.cz> (raw)
In-Reply-To: <20210414151850.GG3697@techsingularity.net>

On 4/14/21 5:18 PM, Mel Gorman wrote:
> On Wed, Apr 14, 2021 at 02:56:45PM +0200, Vlastimil Babka wrote:
>> So it seems that this intermediate assignment to zone counters (using
>> atomic_long_set() even) is unnecessary and this could mimic sum_vm_events() that
>> just does the summation on a local array?
>> 
> 
> The atomic is unnecessary for sure but using a local array is
> problematic because of your next point.

IIUC vm_events seems to do fine without a centralized array and handling CPU hot
remove at the sime time ...

>> And probably a bit more serious is that vm_events have vm_events_fold_cpu() to
>> deal with a cpu going away, but after your patch the stats counted on a cpu just
>> disapepar from the sums as it goes offline as there's no such thing for the numa
>> counters.
>> 
> 
> That is a problem I missed. Even if zonestats was preserved on
> hot-remove, fold_vm_zone_numa_events would not be reading the CPU so
> hotplug events jump all over the place.
> 
> So some periodic folding is necessary. I would still prefer not to do it
> by time but it could be done only on overflow or when a file like
> /proc/vmstat is read. I'll think about it a bit more and see what I come
> up with.

... because vm_events_fold_cpu() seems to simply move the stats from the CPU
being offlined to the current one. So the same approach should be enough for
NUMA stats?

> Thanks!
> 


  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-07 20:24 [PATCH 0/11 v2] Use local_lock for pcp protection and reduce stat overhead Mel Gorman
2021-04-07 20:24 ` [PATCH 01/11] mm/page_alloc: Split per cpu page lists and zone stats Mel Gorman
2021-04-12 17:43   ` Vlastimil Babka
2021-04-13 13:27     ` Mel Gorman
2021-04-07 20:24 ` [PATCH 02/11] mm/page_alloc: Convert per-cpu list protection to local_lock Mel Gorman
2021-04-08 10:52   ` Peter Zijlstra
2021-04-08 17:42     ` Mel Gorman
2021-04-09  6:39       ` Peter Zijlstra
2021-04-09  7:59         ` Mel Gorman
2021-04-09  8:24           ` Peter Zijlstra
2021-04-09 13:32             ` Mel Gorman
2021-04-09 18:55               ` Peter Zijlstra
2021-04-12 11:56                 ` Mel Gorman
2021-04-12 21:47                   ` Thomas Gleixner
2021-04-13 16:52                     ` Mel Gorman
2021-04-07 20:24 ` [PATCH 03/11] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove Mel Gorman
2021-04-07 20:24 ` [PATCH 04/11] mm/vmstat: Convert NUMA statistics to basic NUMA counters Mel Gorman
2021-04-14 12:56   ` Vlastimil Babka
2021-04-14 15:18     ` Mel Gorman
2021-04-14 15:56       ` Vlastimil Babka [this message]
2021-04-15 10:06         ` Mel Gorman
2021-04-07 20:24 ` [PATCH 05/11] mm/vmstat: Inline NUMA event counter updates Mel Gorman
2021-04-07 20:24 ` [PATCH 06/11] mm/page_alloc: Batch the accounting updates in the bulk allocator Mel Gorman
2021-04-07 20:24 ` [PATCH 07/11] mm/page_alloc: Reduce duration that IRQs are disabled for VM counters Mel Gorman
2021-04-07 20:24 ` [PATCH 08/11] mm/page_alloc: Remove duplicate checks if migratetype should be isolated Mel Gorman
2021-04-07 20:24 ` [PATCH 09/11] mm/page_alloc: Explicitly acquire the zone lock in __free_pages_ok Mel Gorman
2021-04-07 20:24 ` [PATCH 10/11] mm/page_alloc: Avoid conflating IRQs disabled with zone->lock Mel Gorman
2021-04-07 20:24 ` [PATCH 11/11] mm/page_alloc: Update PGFREE outside the zone lock in __free_pages_ok Mel Gorman
2021-04-08 10:56 ` [PATCH 0/11 v2] Use local_lock for pcp protection and reduce stat overhead Peter Zijlstra
2021-04-08 17:48   ` Mel Gorman

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