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Re: [Qemu-devel] [PATCHv2 2/2] migration: do not overwrite zero pages
From: |
mdroth |
Subject: |
Re: [Qemu-devel] [PATCHv2 2/2] migration: do not overwrite zero pages |
Date: |
Mon, 10 Jun 2013 11:10:29 -0500 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Jun 10, 2013 at 12:14:20PM +0200, Peter Lieven wrote:
> on incoming migration do not memset pages to zero if they already read as
> zero.
> this will allocate a new zero page and consume memory unnecessarily. even
> if we madvise a MADV_DONTNEED later this will only deallocate the memory
> asynchronously.
>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> arch_init.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index 08fccf6..cf4e1d5 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -832,14 +832,16 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> }
>
> ch = qemu_get_byte(f);
> - memset(host, ch, TARGET_PAGE_SIZE);
> + if (ch != 0 || !is_zero_page(host)) {
> + memset(host, ch, TARGET_PAGE_SIZE);
> #ifndef _WIN32
> - if (ch == 0 &&
> - (!kvm_enabled() || kvm_has_sync_mmu()) &&
> - getpagesize() <= TARGET_PAGE_SIZE) {
> - qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
> - }
> + if (ch == 0 &&
> + (!kvm_enabled() || kvm_has_sync_mmu()) &&
> + getpagesize() <= TARGET_PAGE_SIZE) {
> + qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
> + }
Reviewed-by: Michael Roth <address@hidden>
Also CC'ing qemu-stable, but from what I gather this just mitigates the
performance impact of 1/2 and isn't strictly necessary to fix migration?
i.e. we can still do outgoing migration to 1.5.0 guests?
> #endif
> + }
> } else if (flags & RAM_SAVE_FLAG_PAGE) {
> void *host;
>
> --
> 1.7.9.5
>
>