From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH] kvm tools: Make the whole guest memory mergeable Date: Fri, 16 Dec 2011 10:45:35 +0200 Message-ID: <1324025135.4496.31.camel@lappy> References: <1323997263-2031-1-git-send-email-zanghongyong@huawei.com> <1324014621.4496.3.camel@lappy> <4EEAED0E.5050106@huawei.com> <1324020188.4496.17.camel@lappy> <4EEB031B.2020806@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-2022-jp" Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, penberg@kernel.org, xiaowei.yang@huawei.com, hanweidong@huawei.com, wusongwei@huawei.com, kongbo@huawei.com To: Zang Hongyong Return-path: Received: from mail-ey0-f174.google.com ([209.85.215.174]:35440 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751229Ab1LPIpm (ORCPT ); Fri, 16 Dec 2011 03:45:42 -0500 Received: by eaaj10 with SMTP id j10so2719139eaa.19 for ; Fri, 16 Dec 2011 00:45:40 -0800 (PST) In-Reply-To: <4EEB031B.2020806@huawei.com> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, 2011-12-16 at 16:36 +0800, Zang Hongyong wrote: > 于 2011/12/16,星期五 15:23, Sasha Levin 写道: > > On Fri, 2011-12-16 at 15:02 +0800, Zang Hongyong wrote: > >> 于 2011/12/16,星期五 13:50, Sasha Levin 写道: > >>> On Fri, 2011-12-16 at 09:01 +0800, zanghongyong@huawei.com wrote: > >>>> If a guest's ram_size exceeds KVM_32BIT_GAP_START, the corresponding kvm tool's > >>>> virtual address size should be (ram_size + KVM_32BIT_GAP_SIZE), rather than ram_size. > >>> You're right. > >>> > >>> There are more places than just the madvise() code which make the same > >>> error you've spotted (for example, the memslot allocation code), so > >>> instead of trying to fix all of them I'd suggest to just update ram_size > >>> in kvm__arch_init() before allocating everything - that should fix all > >>> of them at once. > >>> > >> Yes. There are other scenarios with the same error. > >> However ram_size sometimes means real guest ram size, and sometimes > >> means virtual address > >> size of kvm tool's user space. Shall we define a new variable? > > Let's keep it simple. If the user requests more than RAM than > > KVM_32BIT_GAP_START just increase it by KVM_32BIT_GAP_SIZE, this way > > mapped size == guest size always (we can madvise(MADV_DONTNEED) the gap > > in the mmapped ram). > > > > Since a user which requests more than KVM_32BIT_GAP_START will have to > > be on 64bit host anyway, there shouldn't be any issue with that. > > > Do you mean increase *kvm->ram_size* by KVM_32BIT_GAP_SIZE? > but sometimes kvm->ram_size stands for guest physical ram size (for > example in kvm__init_ram() code). Yup, kvm->ram_size. If the user requested more than KVM_32BIT_GAP_START, we pretty much have to create the gap, so instead of playing around with different interpretations of ram_size, lets add the gap size - this will let us have just one ram_size. mmap()ing extra space for the gap is free, and that was the plan in the first place (we just got the math wrong :) ). Do you see an issue with increasing kvm->ram_size? -- Sasha.