** Changed in: intel
Status: Triaged => Fix Released
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https://bugs.launchpad.net/bugs/1730836
Title:
[Feature] Optimize huge page clear/copy cache behavior
Status in intel:
Fix Released
Status in linux package in Ubuntu:
Fix Released
Bug description:
Description
Huge page helps to reduce TLB miss rate, but it has higher cache
footprint, sometimes this may cause some issue. For example, when
clearing huge page on x86_64 platform, the cache footprint is 2M. But
on a Xeon E5 v3 2699 CPU, there are 18 cores, 36 threads, and only 45M
LLC (last level cache). That is, in average, there are 2.5M LLC for
each core and 1.25M LLC for each thread. If the cache pressure is
heavy when clearing the huge page, and we clear the huge page from the
begin to the end, it is possible that the begin of huge page is
evicted from the cache after we finishing clearing the end of the huge
page. And it is possible for the application to access the begin of
the huge page after clearing the huge page.
To help the above situation, when we clear or copy a huge page, the
order to clear or copy the sub-pages can be changed to clear or copy
the sub-page to access last.
Target Kernel: 4,19
Target Release: 18.10
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