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Re: [Qemu-devel] [PATCH v4 08/11] kvm: Persistent per kvmslot dirty bitm
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v4 08/11] kvm: Persistent per kvmslot dirty bitmap |
Date: |
Mon, 3 Jun 2019 10:49:14 +0100 |
User-agent: |
Mutt/1.11.4 (2019-03-13) |
* Peter Xu (address@hidden) wrote:
> When synchronizing dirty bitmap from kernel KVM we do it in a
> per-kvmslot fashion and we allocate the userspace bitmap for each of
> the ioctl. This patch instead make the bitmap cache be persistent
> then we don't need to g_malloc0() every time.
>
> More importantly, the cached per-kvmslot dirty bitmap will be further
> used when we want to add support for the KVM_CLEAR_DIRTY_LOG and this
> cached bitmap will be used to guarantee we won't clear any unknown
> dirty bits otherwise that can be a severe data loss issue for
> migration code.
>
> Signed-off-by: Peter Xu <address@hidden>
OK, so this will use a little more memory, but probably fragment stuff
less.
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> ---
> accel/kvm/kvm-all.c | 10 +++++++---
> include/sysemu/kvm_int.h | 2 ++
> 2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index b686531586..9fb0694772 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -511,17 +511,19 @@ static int
> kvm_physical_sync_dirty_bitmap(KVMMemoryListener *kml,
> */
> size = ALIGN(((mem->memory_size) >> TARGET_PAGE_BITS),
> /*HOST_LONG_BITS*/ 64) / 8;
> - d.dirty_bitmap = g_malloc0(size);
> + if (!mem->dirty_bmap) {
> + /* Allocate on the first log_sync, once and for all */
> + mem->dirty_bmap = g_malloc0(size);
> + }
>
> + d.dirty_bitmap = mem->dirty_bmap;
> d.slot = mem->slot | (kml->as_id << 16);
> if (kvm_vm_ioctl(s, KVM_GET_DIRTY_LOG, &d) == -1) {
> DPRINTF("ioctl failed %d\n", errno);
> - g_free(d.dirty_bitmap);
> return -1;
> }
>
> kvm_get_dirty_pages_log_range(section, d.dirty_bitmap);
> - g_free(d.dirty_bitmap);
> }
>
> return 0;
> @@ -796,6 +798,8 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
> }
>
> /* unregister the slot */
> + g_free(mem->dirty_bmap);
> + mem->dirty_bmap = NULL;
> mem->memory_size = 0;
> mem->flags = 0;
> err = kvm_set_user_memory_region(kml, mem, false);
> diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
> index f838412491..687a2ee423 100644
> --- a/include/sysemu/kvm_int.h
> +++ b/include/sysemu/kvm_int.h
> @@ -21,6 +21,8 @@ typedef struct KVMSlot
> int slot;
> int flags;
> int old_flags;
> + /* Dirty bitmap cache for the slot */
> + unsigned long *dirty_bmap;
> } KVMSlot;
>
> typedef struct KVMMemoryListener {
> --
> 2.17.1
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] [PATCH v4 01/11] migration: No need to take rcu during sync_dirty_bitmap, (continued)
- [Qemu-devel] [PATCH v4 01/11] migration: No need to take rcu during sync_dirty_bitmap, Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 02/11] memory: Remove memory_region_get_dirty(), Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 03/11] memory: Don't set migration bitmap when without migration, Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 04/11] bitmap: Add bitmap_copy_with_{src|dst}_offset(), Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 05/11] memory: Pass mr into snapshot_and_clear_dirty, Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 06/11] memory: Introduce memory listener hook log_clear(), Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 07/11] kvm: Update comments for sync_dirty_bitmap, Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 08/11] kvm: Persistent per kvmslot dirty bitmap, Peter Xu, 2019/06/03
- Re: [Qemu-devel] [PATCH v4 08/11] kvm: Persistent per kvmslot dirty bitmap,
Dr. David Alan Gilbert <=
- [Qemu-devel] [PATCH v4 09/11] kvm: Introduce slots lock for memory listener, Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 10/11] kvm: Support KVM_CLEAR_DIRTY_LOG, Peter Xu, 2019/06/03
- [Qemu-devel] [PATCH v4 11/11] migration: Split log_clear() into smaller chunks, Peter Xu, 2019/06/03