From: Minchan Kim <minchan@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
<linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
Subject: Re: [PATCH] mm: fix pgalloc_stall on unpopulated zone
Date: Thu, 14 Jul 2016 10:11:19 +0900 [thread overview]
Message-ID: <20160714011119.GA23512@bbox> (raw)
In-Reply-To: <20160713092504.GJ11400@suse.de>
On Wed, Jul 13, 2016 at 10:25:04AM +0100, Mel Gorman wrote:
> On Wed, Jul 13, 2016 at 11:24:13AM +0900, Minchan Kim wrote:
> > If we use sc->reclaim_idx for accounting pgstall, it can increase
> > the count on unpopulated zone, for example, movable zone(but
> > my system doesn't have movable zone) if allocation request were
> > GFP_HIGHUSER_MOVABLE. It doesn't make no sense.
> >
>
> I wanted to track the highest zone allowed by each allocation regardless
> of what the zone population state was. Otherwise, consider the following
> on a NUMA system
>
> 1. An allocation request arrives for GFP_HIGHUSER_MOVABLE that stalls
> 2. System has two nodes, node 0 with ZONE_NORMAL, node 1 with ZONE_HIGHMEM
> 3. If the allocating process is on node 0, the stall is accounted on ZONE_NORMAL
> 4. If the allocatinn process is on node 1, the stall is accounted on ZONE_HIGHMEM
>
> Multiple runs of the same workload on the same machine will see stall
> statistics on different zones and renders the stat useless. This is
> difficult to analyse because stalls accounted for on ZONE_NORMAL may or
> may not be zone-constrained allocations.
Fair enough.
For the allocstall, it would be better to show the requested zone.
>
> The patch means that the vmstat accounting and tracepoint data is also
> out of sync. One thing I wanted to be able to do was
>
> 1. Observe that there are alloc stalls on DMA32 or some other low zone
> 2. Activate mm_vmscan_direct_reclaim_begin, filter on classzone_idx ==
> DMA32 and identify the source of the lowmem allocations
>
> If your patch is applied, I cannot depend on the stall stats any more
> and the tracepoint is required to determine if there really any
> zone-contrained allocations. It can be *inferred* from the skip stats
> but only if such skips occurred and that is not guaranteed.
Just a nit:
Hmm, can't we omit classzone_idx in mm_vm_scan_direct_begin_template?
Because every functions already have gfp_flags so that we can classzone_idx
via gfp_zone(gfp_flags) without passing it.
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2016-07-14 1:10 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-13 2:24 [PATCH] mm: fix pgalloc_stall on unpopulated zone Minchan Kim
2016-07-13 9:25 ` Mel Gorman
2016-07-14 1:11 ` Minchan Kim [this message]
2016-07-14 8:51 ` Mel Gorman
2016-07-14 8:58 ` Minchan Kim
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