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SubjectRe: [PATCH 4/5] mm/vmstat.c: move the per-node stats to the front of /proc/zoneinfo
On 03/24/20 at 12:25pm, David Rientjes wrote:
> On Tue, 24 Mar 2020, Baoquan He wrote:
>
> > This moving makes the layout of /proc/zoneinfo more sensible. And there
> > are 4 zones at most currently, it doesn't need to scroll down much to get
> > to the 1st populated zone, even though the 1st populated zone is MOVABLE
> > zone.
> >
>
> Doesn't this introduce risk that it will break existing parsers of
> /proc/zoneinfo in subtle ways?
>
> In some cases /proc/zoneinfo is a tricky file to correctly parse because
> you have to rely on the existing order in which it is printed to determine
> which zone is being described. We need to print zones even with unmanaged
> pages, for instance, otherwise userspace may be unaware of which zones are
> supported and what order they are in. That's important to be able to
> construct the proper string to use when writing vm.lowmem_reserve_ratio.
>
> I'd prefer not changing the order of /proc/zoneinfo if it can be avoided
> just because the risk outweighs the reward that we may break some
> initscript parsers.

Oh, I may not describe the change and result clearly. This patch doesn't
change zone order at all. I only move the per-node stats to the front of
each node, the zone order is completely kept the same, still DMA, DMA32,
NORMAL, MOVABLE.

Before this patch, per-node stats are printed inside the first populated
zone of each node. E.g in this node 2 which only has movable zone, the
per-node stats is embedded in the last zone. In fact, this per-node stats
are made for the whole node, but not for one zone.

Node 2, zone DMA
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 0, 1024, 1024)
Node 2, zone DMA32
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 0, 1024, 1024)
Node 2, zone Normal
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
protection: (0, 0, 0, 8192, 8192)
Node 2, zone Movable
per-node stats --------------------------->> start of per-node stats
nr_inactive_anon 42
nr_active_anon 11787
nr_inactive_file 32222
nr_active_file 6081
nr_unevictable 0
nr_slab_reclaimable 0
nr_slab_unreclaimable 0
...... --------- (mid items are omitted)
nr_anon_transparent_hugepages 0
nr_unstable 0
nr_vmscan_write 0
nr_vmscan_immediate_reclaim 0
nr_dirtied 25523
nr_written 25113
nr_kernel_misc_reclaimable 0 ------------------------->> end of per-node stats
pages free 211331 ------------------------->> start printing data of zone Movable
min 3524
low 4405
high 5286
spanned 262144
present 262144
managed 262144
protection: (0, 0, 0, 0, 0)
nr_free_pages 211331
nr_zone_inactive_anon 42
nr_zone_active_anon 11787
nr_zone_inactive_file 32222
nr_zone_active_file 6081
nr_zone_unevictable 0
nr_zone_write_pending 2

With this patch applied, only the per-node stats part is moved to the
front of each node.

Node 2, per-node stats --------------------------->> start of per-node stats
nr_inactive_anon 42
nr_active_anon 12358
nr_inactive_file 33139
nr_active_file 10088
nr_unevictable 0
nr_slab_reclaimable 0
...... --------- (mid items are omitted)
nr_vmscan_write 0
nr_vmscan_immediate_reclaim 0
nr_dirtied 9082
nr_written 8844
nr_kernel_misc_reclaimable 0
nr_foll_pin_acquired 0
nr_foll_pin_released 0 ------------------------->> end of per-node stats
Node 2, zone DMA
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
Node 2, zone DMA32
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
Node 2, zone Normal
pages free 0
min 0
low 0
high 0
spanned 0
present 0
managed 0
Node 2, zone Movable
pages free 205601 ------------------------->> start printing data of zone Movable
min 3525
low 4406
high 5287
spanned 262144
present 262144
managed 262144
protection: (0, 0, 0, 0)
nr_free_pages 205601
nr_zone_inactive_anon 42
nr_zone_active_anon 12358
........

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