From: David Gibson <david@gibson.dropbear.id.au>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: dhildenb@redhat.com, imammedo@redhat.com, ehabkost@redhat.com,
pbonzini@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org,
mst@redhat.com
Subject: Re: [Qemu-devel] [RFC 1/5] virtio-balloon: Remove unnecessary MADV_WILLNEED on deflate
Date: Sat, 13 Oct 2018 17:23:51 +1100 [thread overview]
Message-ID: <20181013062351.GC16167@umbus.fritz.box> (raw)
In-Reply-To: <364642df-1e17-dbea-1cec-a5cf6c606b27@linaro.org>
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On Fri, Oct 12, 2018 at 10:41:33AM -0700, Richard Henderson wrote:
> 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
> whatever?
As Eric notes, I think you have inflate and deflate the wrong way around.
> 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.
>
>
> r~
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2018-10-13 6:41 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-12 3:24 [Qemu-devel] [RFC 0/5] Improve balloon handling of pagesizes other than 4kiB David Gibson
2018-10-12 3:24 ` [Qemu-devel] [RFC 1/5] virtio-balloon: Remove unnecessary MADV_WILLNEED on deflate David Gibson
2018-10-12 7:40 ` David Hildenbrand
2018-10-13 6:26 ` David Gibson
2018-10-12 17:41 ` Richard Henderson
2018-10-12 17:59 ` Eric Blake
2018-10-13 6:23 ` David Gibson [this message]
2018-10-12 18:05 ` Michael S. Tsirkin
2018-10-15 6:54 ` David Hildenbrand
2018-10-15 10:43 ` Michael S. Tsirkin
2018-10-15 11:14 ` David Hildenbrand
2018-12-04 4:26 ` David Gibson
2018-10-12 3:24 ` [Qemu-devel] [RFC 2/5] virtio-balloon: Corrections to address verification David Gibson
2018-10-12 7:44 ` David Hildenbrand
2018-10-13 6:25 ` David Gibson
2018-10-12 3:24 ` [Qemu-devel] [RFC 3/5] virtio-balloon: Rework ballon_page() interface David Gibson
2018-10-12 7:46 ` David Hildenbrand
2018-10-13 6:29 ` David Gibson
2018-10-12 3:24 ` [Qemu-devel] [RFC 4/5] virtio-balloon: Use ram_block_discard_range() instead of raw madvise() David Gibson
2018-10-12 3:24 ` [Qemu-devel] [RFC 5/5] virtio-balloon: Safely handle BALLOON_PAGE_SIZE < host page size David Gibson
2018-10-12 8:06 ` David Hildenbrand
2018-10-13 6:40 ` David Gibson
2018-10-15 7:08 ` David Hildenbrand
2018-10-17 3:28 ` David Gibson
2018-10-17 9:56 ` David Hildenbrand
2018-10-23 8:02 ` David Gibson
2018-10-23 15:13 ` David Hildenbrand
2018-10-12 8:32 ` David Hildenbrand
2018-10-13 6:41 ` David Gibson
2018-10-12 17:26 ` [Qemu-devel] [RFC 0/5] Improve balloon handling of pagesizes other than 4kiB Michael S. Tsirkin
2018-10-17 3:31 ` David Gibson
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