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Re: [Qemu-block] [PATCH v5 04/10] block: Support meta dirty bitmap
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH v5 04/10] block: Support meta dirty bitmap |
Date: |
Wed, 22 Jun 2016 17:53:15 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
On 03.06.2016 06:32, Fam Zheng wrote:
> The added group of operations enables tracking of the changed bits in
> the dirty bitmap.
>
> Signed-off-by: Fam Zheng <address@hidden>
> ---
> block/dirty-bitmap.c | 52
> ++++++++++++++++++++++++++++++++++++++++++++
> include/block/dirty-bitmap.h | 9 ++++++++
> 2 files changed, 61 insertions(+)
>
> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
> index 628b77c..9c53c56 100644
> --- a/block/dirty-bitmap.c
> +++ b/block/dirty-bitmap.c
> @@ -38,6 +38,7 @@
> */
> struct BdrvDirtyBitmap {
> HBitmap *bitmap; /* Dirty sector bitmap implementation */
> + HBitmap *meta; /* Meta dirty bitmap */
> BdrvDirtyBitmap *successor; /* Anonymous child; implies frozen status */
> char *name; /* Optional non-empty unique ID */
> int64_t size; /* Size of the bitmap (Number of sectors) */
> @@ -103,6 +104,56 @@ BdrvDirtyBitmap
> *bdrv_create_dirty_bitmap(BlockDriverState *bs,
> return bitmap;
> }
>
> +/* bdrv_create_meta_dirty_bitmap
> + *
> + * Create a meta dirty bitmap that tracks the changes of bits in @bitmap.
> I.e.
> + * when a dirty status bit in @bitmap is changed (either from reset to set or
> + * the other way around), its respective meta dirty bitmap bit will be marked
> + * dirty as well.
Not wrong, but I'd like a note here that this is not an
when-and-only-when relationship, i.e. that bits in the meta bitmap may
be set even without the tracked bits in the dirty bitmap having changed.
Maybe this should be mentioned somewhere in patch 2, too. Or maybe only
in patch 2.
> + *
> + * @bitmap: the block dirty bitmap for which to create a meta dirty bitmap.
> + * @chunk_size: how many bytes of bitmap data does each bit in the meta
> bitmap
> + * track.
> + */
> +void bdrv_create_meta_dirty_bitmap(BdrvDirtyBitmap *bitmap,
> + int chunk_size)
> +{
> + assert(!bitmap->meta);
> + bitmap->meta = hbitmap_create_meta(bitmap->bitmap,
> + chunk_size * BITS_PER_BYTE);
> +}
> +
> +void bdrv_release_meta_dirty_bitmap(BdrvDirtyBitmap *bitmap)
> +{
> + assert(bitmap->meta);
> + hbitmap_free_meta(bitmap->bitmap);
> + bitmap->meta = NULL;
> +}
> +
> +int bdrv_dirty_bitmap_get_meta(BlockDriverState *bs,
> + BdrvDirtyBitmap *bitmap, int64_t sector,
> + int nb_sectors)
> +{
> + uint64_t i;
> + int gran = bdrv_dirty_bitmap_granularity(bitmap) >> BDRV_SECTOR_BITS;
> +
> + /* To optimize: we can make hbitmap to internally check the range in a
> + * coarse level, or at least do it word by word. */
We could also multiply gran by the granularity of the meta bitmap. Each
bit of the meta bitmap tracks at least eight bits of the dirty bitmap,
so we're calling hbitmap_get() at least eight times as often as
necessary here.
Or we just use int gran = hbitmap_granularity(bitmap->meta);.
Not exactly wrong, though, so:
Reviewed-by: Max Reitz <address@hidden>
> + for (i = sector; i < sector + nb_sectors; i += gran) {
> + if (hbitmap_get(bitmap->meta, i)) {
> + return true;
> + }
> + }
> + return false;
> +}
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- [Qemu-block] [PATCH v5 00/10] Dirty bitmap changes for migration/persistence work, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 03/10] tests: Add test code for meta bitmap, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 01/10] block: Hide HBitmap in block dirty bitmap interface, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 06/10] block: Assert that bdrv_release_dirty_bitmap succeeded, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 04/10] block: Support meta dirty bitmap, Fam Zheng, 2016/06/03
- Re: [Qemu-block] [PATCH v5 04/10] block: Support meta dirty bitmap,
Max Reitz <=
- [Qemu-block] [PATCH v5 02/10] HBitmap: Introduce "meta" bitmap to track bit changes, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 05/10] block: Add two dirty bitmap getters, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 07/10] hbitmap: serialization, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 08/10] block: BdrvDirtyBitmap serialization interface, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 10/10] block: More operations for meta dirty bitmap, Fam Zheng, 2016/06/03
- [Qemu-block] [PATCH v5 09/10] tests: Add test code for hbitmap serialization, Fam Zheng, 2016/06/03
- Re: [Qemu-block] [Qemu-devel] [PATCH v5 00/10] Dirty bitmap changes for migration/persistence work, Fam Zheng, 2016/06/03