From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
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: Thu, 15 Apr 2021 11:06:50 +0100 [thread overview]
Message-ID: <20210415100650.GJ3697@techsingularity.net> (raw)
In-Reply-To: <c4dff8a5-7959-c191-c66d-23a515244b80@suse.cz>
On Wed, Apr 14, 2021 at 05:56:53PM +0200, Vlastimil Babka wrote:
> 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 ...
>
The vm_events are more global in nature. They are not reported
to userspace on a per-zone (/proc/zoneinfo) basis or per-node
(/sys/devices/system/node/node*/numastat) basis so they are not equivalent.
> >> 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?
>
Yes, or at least very similar.
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2021-04-15 10:06 UTC|newest]
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
2021-04-15 10:06 ` Mel Gorman [this message]
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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