commit a5a03facba31c9ab7b991c3761c68ec831a05c00
author Nick Maniscalco <maniscalco@google.com> Fri Apr 19 23:42:47 2019 +0000
committer CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org> Fri Apr 19 23:42:47 2019 +0000
tree 67dc1839ccb9c8d1c11e217d9bc79017e6265604
parent 9c5edda25e6617080637195e1b1a43c7da74440d

[kernel][vm] Keep per cpu counts of vm_page states

The purpose of this change is to improve the performance of
ZX_INFO_KMEM_STATS.  By maintaining counters of vm_page states we no
longer need to walk all pages to compute ZX_INFO_KMEM_STATS.

A previous version of this change used global atomic integers, but
that proved to be too expensive (ZX-3916).  Instead, we use per cpu
counters and access them with preemption disabled.

Move vm_page_state to it's own file to prevent a cicular dependency
between page and percpu.

Add a couple static helper methods to Percpus to facilitate accessing
per cpu counters like vm_page_counts.

Ran zircon_benchmarks on a NUC to ensure this doesn't significantly
regress performance.  Looked at Channel/WriteRead/64bytes as it seems
to be a bellwether.

Before --

      Mean    Std dev        Min        Max     Median Unit         Mean Mbytes/sec Test case
       562         33        542       6403        555 nanoseconds          108.552 Channel/WriteRead/64bytes
       277         19        263       4391        272 nanoseconds              N/A Channel/WriteRead/64bytes.write
       285         17        274       2680        282 nanoseconds              N/A Channel/WriteRead/64bytes.read

After --

      Mean    Std dev        Min        Max     Median Unit         Mean Mbytes/sec Test case
       571         13        558       6263        569 nanoseconds          106.880 Channel/WriteRead/64bytes
       284         10        275       4458        282 nanoseconds              N/A Channel/WriteRead/64bytes.write
       287          7        279       1805        286 nanoseconds              N/A Channel/WriteRead/64bytes.read

Bug: ZX-833 #comment per cpu counts
Test: booted and ran 'kstats -m'
Change-Id: I18083c4dbc3d0423cc59cf3700a93dc72de8d2e3