From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47292) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VT7Lr-0000nP-96 for qemu-devel@nongnu.org; Mon, 07 Oct 2013 05:43:47 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VT7Lm-0004TU-ND for qemu-devel@nongnu.org; Mon, 07 Oct 2013 05:43:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43710) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VT7Lm-0004TE-Ab for qemu-devel@nongnu.org; Mon, 07 Oct 2013 05:43:38 -0400 Message-ID: <5252823A.5050500@redhat.com> Date: Mon, 07 Oct 2013 11:43:22 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1381137738-4231-1-git-send-email-pl@kamp.de> In-Reply-To: <1381137738-4231-1-git-send-email-pl@kamp.de> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] migration: drop MADVISE_DONT_NEED for incoming zero pages List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Lieven Cc: quintela@redhat.com, qemu-devel@nongnu.org, xiaoguangrong@linux.vnet.ibm.com Il 07/10/2013 11:22, Peter Lieven ha scritto: > The madvise for zeroed out pages was introduced when every transferred > zero page was memset to zero and thus allocated. Since commit > 211ea740 we check for zeroness of a target page before we memset > it to zero. Additionally we memmap target memory so it is essentially > zero initalized (except for e.g. option roms and bios which are loaded > into target memory altough they shouldn't). > > It was reported recently that this madvise causes a performance degradation > in some situations. As the madvise should only be called rarely and if its called > it is likely on a busy page (it was non-zero and changed to zero during migration) > drop it completely. > > Signed-off-by: Peter Lieven > Reported-By: Zhang Haoyu > --- > arch_init.c | 8 -------- > 1 file changed, 8 deletions(-) > > diff --git a/arch_init.c b/arch_init.c > index 7545d96..e0acbc5 100644 > --- a/arch_init.c > +++ b/arch_init.c > @@ -850,14 +850,6 @@ void ram_handle_compressed(void *host, uint8_t ch, uint64_t size) > { > if (ch != 0 || !is_zero_range(host, size)) { > memset(host, ch, size); > -#ifndef _WIN32 > - if (ch == 0 && (!kvm_enabled() || kvm_has_sync_mmu())) { > - size = size & ~(getpagesize() - 1); > - if (size > 0) { > - qemu_madvise(host, size, QEMU_MADV_DONTNEED); > - } > - } > -#endif > } > } > > Acked-by: Paolo Bonzini