On 08/10/20 at 03:46pm, Yu Zhao wrote:
> On Mon, Aug 10, 2020 at 02:24:03PM -0700, Sonny Rao wrote:
> > We (Chrome OS) noticed recently one of our tests started failing on
> > upstream kernels while parsing /proc/zoneinfo
> > I think this patch is the cause:
> >
> > 26e7deadaae17 mm/vmstat.c: do not show lowmem reserve protection
> > information of empty zone
> >
> > Maybe our parser was being overly strict by looking for the protection
> > line, and it's not hard to fix but raised the question of whether there's
> > any ABI compatibility guarantees about these files?
>
> According to Documentation/admin-guide/sysctl/vm.rst, "Each zone has
> an array of protection pages". I'm not sure if this is the guarantee,
> but the doc should reflect the actual format.
The current code will list all zones in one memory node, even though
that node only has one existing zone. E.g in below node 1,
it only has NORMAL zone, but we will list zone DMA, DMA32, MOVABLE,
DEVICE which are all empty zone, namely doesn't exist. So, each zone
has an array of protection pages, it should not include the nonexistent
zone. I thought nobody would check the protection line of an empty zone,
seems I was wrong.
(Note that below /proc/zoneinfo is from an old system, protection line
is still existing for empty zone)
Node 1, zone DMA
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 61854, 61854, 61854)
Node 1, zone DMA32
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 61854, 61854, 61854)
Node 1, zone Normal
per-node stats
nr_inactive_anon 259
nr_active_anon 11926
...
nr_written 0
nr_kernel_misc_reclaimable 0
pages free 16206452
pages free 16206452
min 11280
low 27114
high 42948
spanned 16777216
present 16777216
managed 15834637
protection: (0, 0, 0, 0, 0)
...
Node 1, zone Movable
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 0, 0, 0)
Node 1, zone Device
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 0, 0, 0)
>
