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From: Richard Henderson <richard.henderson@linaro.org>
To: David Gibson <david@gibson.dropbear.id.au>,
	dhildenb@redhat.com, imammedo@redhat.com, ehabkost@redhat.com
Cc: 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: Fri, 12 Oct 2018 10:41:33 -0700	[thread overview]
Message-ID: <364642df-1e17-dbea-1cec-a5cf6c606b27@linaro.org> (raw)
In-Reply-To: <20181012032431.32693-2-david@gibson.dropbear.id.au>

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?

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~

  parent reply	other threads:[~2018-10-12 17:41 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 [this message]
2018-10-12 17:59     ` Eric Blake
2018-10-13  6:23     ` David Gibson
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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