Re: [PATCH 27/27] mm: vmstat: Account per-zone stalls and pages skipped during reclaim

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On 06/09/2016 08:04 PM, Mel Gorman wrote:
The vmstat allocstall was fairly useful in the general sense but
node-based LRUs change that. It's important to know if a stall was for an
address-limited allocation request as this will require skipping pages from
other zones. This patch adds pgstall_* counters to replace allocstall. The
sum of the counters will equal the old allocstall so it can be trivially
recalculated. A high number of address-limited allocation requests may
result in a lot of useless LRU scanning for suitable pages.

As address-limited allocations require pages to be skipped, it's important
to know how much useless LRU scanning took place so this patch adds
pgskip* counters. This yields the following model

1. The number of address-space limited stalls can be accounted for (pgstall)
2. The amount of useless work required to reclaim the data is accounted (pgskip)
3. The total number of scans is available from pgscan_kswapd and pgscan_direct
   so from that the ratio of useful to useless scans can be calculated.

Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

Nice work!

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