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Re: [Qemu-ppc] [Qemu-devel] [RFC 1/5] virtio-balloon: Remove unnecessary
Re: [Qemu-ppc] [Qemu-devel] [RFC 1/5] virtio-balloon: Remove unnecessary MADV_WILLNEED on deflate
Fri, 12 Oct 2018 10:41:33 -0700
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0
On 10/11/18 8:24 PM, David Gibson wrote:
> When the balloon is inflated, we discard memory place in it using madvise()
> with MADV_DONTNEED. And when we deflate it we use MADV_WILLNEED, which
> sounds like it makes sense but is actually unnecessary.
> The misleadingly named MADV_DONTNEED just discards the memory in question,
> it doesn't set any persistent state on it in-kernel; all that's necessary
> to bring the memory back is to touch it.
Isn't the point of deflate to free up host memory, for use by other guests or
If you do nothing upon deflate, then that doesn't actually happen. It seems to
me that this is backward and you should use DONTNEED on deflate and then
inflate should do nothing.
[Qemu-ppc] [RFC 4/5] virtio-balloon: Use ram_block_discard_range() instead of raw madvise(), David Gibson, 2018/10/11
[Qemu-ppc] [RFC 5/5] virtio-balloon: Safely handle BALLOON_PAGE_SIZE < host page size, David Gibson, 2018/10/11