Messages in this thread | | | Date | Wed, 09 Sep 2020 13:27:42 +0200 | From | osalvador@suse ... | Subject | Re: [RFC 0/5] disable pcplists during page isolation |
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On 2020-09-09 12:54, Vlastimil Babka wrote: > Thanks! I expect no performance change while no isolation is in > progress, as > there are no new tests added in alloc/free paths. During page isolation > there's > a single drain instead of once-per-pageblock, which is a benefit. But > the > pcplists are effectively disabled for the whole of online_pages(), > offline_pages() or alloc_contig_range(), which will affect parallel > page > allocator users. It depends on how long these operations take and how > heavy the > parallel usage is, so I have no good answers. Might be similar to the > current > periodic drain.
I have seen some systems taking quite some time when offlining sections due to the migration of the respective pages not being that smooth and having do_migrate_range to do some spins. But to be fair, online_pages and offline_pages are not routines that get called that often, and we would be safe to assume that memory-hotplug operations are not constantly happening, but are rather one-offs operations.
I am not sure about Xen and HV, IIRC Xen was using online_pages and offline_pages routines to do the ballooning?
I will dive in this in the following days, thanks for the work Vlastimil
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