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Tue, 15 Dec 2020 09:57:21 -0800 (PST) X-Google-Smtp-Source: ABdhPJx8bfPuUic5IlFaMqNkLeT2QVRTv2MUhxj5amypjjTNH37ZermwlcZksjXs5Y7lW2zsVq9Skg== X-Received: by 2002:a37:9b8d:: with SMTP id d135mr37695633qke.338.1608055041698; Tue, 15 Dec 2020 09:57:21 -0800 (PST) Received: from xz-x1 ([142.126.83.202]) by smtp.gmail.com with ESMTPSA id c28sm9952166qtv.2.2020.12.15.09.57.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Dec 2020 09:57:21 -0800 (PST) Date: Tue, 15 Dec 2020 12:57:19 -0500 From: Peter Xu To: Keqian Zhu Subject: Re: [PATCH 1/2] accel: kvm: Fix memory waste under mismatch page size Message-ID: <20201215175719.GA112585@xz-x1> References: <20201215071948.23940-1-zhukeqian1@huawei.com> <20201215071948.23940-2-zhukeqian1@huawei.com> MIME-Version: 1.0 In-Reply-To: <20201215071948.23940-2-zhukeqian1@huawei.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , jiangkunkun@huawei.com, qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , qemu-arm@nongnu.org, Paolo Bonzini , Zenghui Yu , wanghaibin.wang@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Dec 15, 2020 at 03:19:47PM +0800, Keqian Zhu wrote: > When handle dirty log, we face qemu_real_host_page_size and > TARGET_PAGE_SIZE. The first one is the granule of KVM dirty > bitmap, and the second one is the granule of QEMU dirty bitmap. > > Generally speaking, qemu_real_host_page_size >= TARGET_PAGE_SIZE, > so misuse TARGET_PAGE_SIZE to init kvmslot dirty_bmap may waste > memory. For example, when qemu_real_host_page_size is 64K and > TARGET_PAGE_SIZE is 4K, this bugfix can save 93.75% memory. > > Signed-off-by: Keqian Zhu > --- > accel/kvm/kvm-all.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c > index baaa54249d..c5e06288eb 100644 > --- a/accel/kvm/kvm-all.c > +++ b/accel/kvm/kvm-all.c > @@ -620,8 +620,12 @@ static void kvm_memslot_init_dirty_bitmap(KVMSlot *mem) > * too, in most cases). > * So for now, let's align to 64 instead of HOST_LONG_BITS here, in > * a hope that sizeof(long) won't become >8 any time soon. > + * > + * Note: the granule of kvm dirty log is qemu_real_host_page_size. > + * And mem->memory_size is aligned to it (otherwise this mem can't > + * be registered to KVM). > */ > - hwaddr bitmap_size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS), > + hwaddr bitmap_size = ALIGN(mem->memory_size / qemu_real_host_page_size, > /*HOST_LONG_BITS*/ 64) / 8; Yes I think this is correct. Thanks. So one thing I failed to notice is cpu_physical_memory_set_dirty_lebitmap() will "amplify" the host dirty pages into guest ones; seems we're all good then. Reviewed-by: Peter Xu -- Peter Xu