Re: [PATCH v2 1/3] powerpc/mm/hash: Avoid resizing-down HPT on first memory hotplug
From: Leonardo Brás <hidden>
Date: 2021-06-09 00:51:42
Also in:
lkml
On Mon, 2021-06-07 at 15:02 +1000, David Gibson wrote:
On Fri, Apr 30, 2021 at 11:36:06AM -0300, Leonardo Bras wrote:quoted
Because hypervisors may need to create HPTs without knowing the guest page size, the smallest used page-size (4k) may be chosen, resulting in a HPT that is possibly bigger than needed. On a guest with bigger page-sizes, the amount of entries for HTP may be too high, causing the guest to ask for a HPT resize-down on the first hotplug. This becomes a problem when HPT resize-down fails, and causes the HPT resize to be performed on every LMB added, until HPT size is compatible to guest memory size, causing a major slowdown. So, avoiding HPT resizing-down on hot-add significantly improves memory hotplug times. As an example, hotplugging 256GB on a 129GB guest took 710s without this patch, and 21s after applied. Signed-off-by: Leonardo Bras <redacted>Sorry it's taken me so long to look at these I don't love the extra statefulness that the 'shrinking' parameter adds, but I can't see an elegant way to avoid it, so: Reviewed-by: David Gibson <redacted>
np, thanks for reviewing! Best regards, Leonardo Bras