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This patch is a revert of 'commit bb01b64cfab7 ("mm/balloon_compaction.c: enqueue zero page to balloon device")' Ballooned pages will be marked as MADV_DONTNEED by the hypervisor and shouldn't be given to the host ksmd to scan. Therefore, it is not necessary to zero ballooned pages, which is very time consuming when the page amount is large. The ongoing fast balloon tests

This patch is a revert of 'commit bb01b64cfab7 ("mm/balloon_compaction.c: enqueue zero page to balloon device")' Ballooned pages will be marked as MADV_DONTNEED by the hypervisor and shouldn't be given to the host ksmd to scan. Therefore, it is not necessary to zero ballooned pages, which is very time consuming when the page amount is large. The ongoing fast balloon tests

...ge. Unfortunately, this assumption is wrong (and it stems from the lack of different page size support in virtio-balloon). Think about these examples: 1. Guest is backed by huge pages (hugetbfs). Ballooning kicks in. MADV_DONTNEED is simply ignored in the hypervisor (hugetlbfs requires fallocate punshhole). Also, trying to zap 4k on e.g. 1MB pages will simply be ignored. 2. Guest on PPC uses 4k pages. Hypervisor uses 64k pages. trying to MADV_DONTNEED 4K on 64k pages will simply be ignored. So unfortunately, zeroing the page is the right thing to do to cover all cases. -- Thanks, David

...ong (and it stems from the > lack of different page size support in virtio-balloon). > > Think about these examples: > > 1. Guest is backed by huge pages (hugetbfs). Ballooning kicks in. > > MADV_DONTNEED is simply ignored in the hypervisor (hugetlbfs requires > fallocate punshhole). Also, trying to zap 4k on e.g. 1MB pages will > simply be ignored. > > 2. Guest on PPC uses 4k pages. Hypervisor uses 64k pages. trying to > MADV_DONTNEED 4K on 64k pages will simply be ignored. > > So unfortunately, zeroing the page is the right thing to do to cover all >...

...ong (and it stems from the > lack of different page size support in virtio-balloon). > > Think about these examples: > > 1. Guest is backed by huge pages (hugetbfs). Ballooning kicks in. > > MADV_DONTNEED is simply ignored in the hypervisor (hugetlbfs requires > fallocate punshhole). Also, trying to zap 4k on e.g. 1MB pages will > simply be ignored. > > 2. Guest on PPC uses 4k pages. Hypervisor uses 64k pages. trying to > MADV_DONTNEED 4K on 64k pages will simply be ignored. > > So unfortunately, zeroing the page is the right thing to do to cover all >...