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David Alan Gilbert" , Andrew Jones , Peter Xu Subject: [PATCH v2 1/2] accel: kvm: Fix memory waste under mismatch page size Date: Thu, 17 Dec 2020 09:49:40 +0800 Message-ID: <20201217014941.22872-2-zhukeqian1@huawei.com> X-Mailer: git-send-email 2.8.4.windows.1 In-Reply-To: <20201217014941.22872-1-zhukeqian1@huawei.com> References: <20201217014941.22872-1-zhukeqian1@huawei.com> MIME-Version: 1.0 X-Originating-IP: [10.174.187.37] X-CFilter-Loop: Reflected Received-SPF: pass client-ip=45.249.212.35; envelope-from=zhukeqian1@huawei.com; helo=szxga07-in.huawei.com X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, 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: jiangkunkun@huawei.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org, Zenghui Yu , wanghaibin.wang@huawei.com, Keqian Zhu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. As qemu_real_host_page_size >= TARGET_PAGE_SIZE (kvm_init() enforced it), 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, it wastes 93.75% (15/16) memory. Signed-off-by: Keqian Zhu Reviewed-by: Andrew Jones Reviewed-by: Peter Xu --- accel/kvm/kvm-all.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- v2 - Address Andrew's comment (qemu_real_host_page_size >= TARGET_PAGE_SIZE is a rule). - Add Andrew and Peter's R-b. diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index 389eaace72..f6b16a8df8 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; mem->dirty_bmap = g_malloc0(bitmap_size); }