Hi Peter, On 2020/12/16 1:57, Peter Xu wrote: > 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 <zhukeqi...@huawei.com> >> --- >> 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 <pet...@redhat.com> > OK Thanks :-)
One more thing, we should consider whether @start and @size is psize aligned (my second patch). Do you agree to add assert on them directly? Thanks, Keqian
