On Thu, Aug 03, 2017 at 07:59:17PM +0800, Wei Wang wrote:
> 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 show that the
> time to balloon 7G pages is increased from ~491ms to 2.8 seconds with
> __GFP_ZERO added. So, this patch removes the flag.
>
> Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Fixes: bb01b64cfab7 ("mm/balloon_compaction.c: enqueue zero page to balloon device")
Looks like hypervisor is better placed to zero these if it wants to.
If it can't for some reason, this change would need a feature bit
to avoid adding extra work for all guests.
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> mm/balloon_compaction.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index 9075aa5..b06d9fe 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -24,7 +24,7 @@ struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info)
> {
> unsigned long flags;
> struct page *page = alloc_page(balloon_mapping_gfp_mask() |
> - __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_ZERO);
> + __GFP_NOMEMALLOC | __GFP_NORETRY);
> if (!page)
> return NULL;
>
> --
> 2.7.4
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