On Thu 20-07-17 09:24:58, Vlastimil Babka wrote:
> On 07/14/2017 10:00 AM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@xxxxxxxx>
> >
> > build_all_zonelists has been (ab)using stop_machine to make sure that
> > zonelists do not change while somebody is looking at them. This is
> > is just a gross hack because a) it complicates the context from which
> > we can call build_all_zonelists (see 3f906ba23689 ("mm/memory-hotplug:
> > switch locking to a percpu rwsem")) and b) is is not really necessary
> > especially after "mm, page_alloc: simplify zonelist initialization".
> >
> > Updates of the zonelists happen very seldom, basically only when a zone
> > becomes populated during memory online or when it loses all the memory
> > during offline. A racing iteration over zonelists could either miss a
> > zone or try to work on one zone twice. Both of these are something we
> > can live with occasionally because there will always be at least one
> > zone visible so we are not likely to fail allocation too easily for
> > example.
> >
> > Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
>
> Some stress testing of this would still be worth, IMHO.
I have run the pathological online/offline of the single memblock in the
movable zone while stressing the same small node with some memory pressure.
Node 1, zone DMA
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 943, 943, 943)
Node 1, zone DMA32
pages free 227310
min 8294
low 10367
high 12440
spanned 262112
present 262112
managed 241436
protection: (0, 0, 0, 0)
Node 1, zone Normal
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 0, 1024)
Node 1, zone Movable
pages free 32722
min 85
low 117
high 149
spanned 32768
present 32768
managed 32768
protection: (0, 0, 0, 0)
root@test1:/sys/devices/system/node/node1# while true
do
echo offline > memory34/state
echo online_movable > memory34/state
done
root@test1:/mnt/data/test/linux-3.7-rc5# numactl --preferred=1 make -j4
and it survived without any unexpected behavior. While this is not
really a great testing coverage it should exercise the allocation path
quite a lot.
I can add this to the changelog if you think it is worth it.
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
--
Michal Hocko
SUSE Labs
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