On 07/31/2017 02:55 PM, Michal Hocko wrote:
On Mon 31-07-17 12:13:33, Wei Wang wrote:
Ballooned pages will be marked as MADV_DONTNEED by the hypervisor and
shouldn't be given to the host ksmd to scan.
Could you point me where this MADV_DONTNEED is done, please?
Sure. It's done in the hypervisor when the balloon pages are received.
Please see line 40 at
https://github.com/qemu/qemu/blob/master/hw/virtio/virtio-balloon.c
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.
Please make it obvious that this is a revert of bb01b64cfab7
("mm/balloon_compaction.c: enqueue zero page to balloon device").
Ok, will do.
Best,
Wei
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