4.15 is now available in Bionic. Marking this Fix Released.
** Tags added: kernel
** Information type changed from Private to Public
** Also affects: linux (Ubuntu Bionic)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Bionic)
Status: New => Fix Released
** Changed in: intel
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/1730879
Title:
[Feature] Increase percpu counter threshold size
Status in intel:
Fix Released
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Bionic:
Fix Released
Bug description:
Description
It was noted that the size of the percpu counters used for
"node/zone_state" is only 8 bytes:
struct per_cpu_pageset {
struct per_cpu_pages pcp;
s8 stat_threshold;
s8 vm_stat_diff[NR_VM_ZONE_STAT_ITEMS];
};
This code is very old. It effectively requires a pair hot, global
cachelines to be touched when the per_cpu counter value does not fit
in "vm_stat_diff".
For this item, we need to increase the size of vm_stat_diff[] from an
s8 to an s16, then allow the ->stat_threshold to be adjusted between
the existing value of 125 and some larger value. Note that the current
threshold from calculate_normal_threshold() is capped at 125 for all
zones over 32GB. We have zones much larger than that today, so it is
likely not scaling optimally.
Target Kernel: 4.14
Target Release: 18.04
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