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

Vlastimil Babka
2016-06-17T12:39:51Z

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@techsingularity.net>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Nice work!