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Re: [Qemu-block] [Qemu-devel] [PATCH v3 1/8] dirty-bitmap: improve bdrv_


From: John Snow
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v3 1/8] dirty-bitmap: improve bdrv_dirty_bitmap_next_zero
Date: Fri, 7 Sep 2018 17:49:00 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0


On 08/14/2018 08:14 AM, Vladimir Sementsov-Ogievskiy wrote:
> Add bytes parameter to the function, to limit searched range.
> 

I'm going to assume that Eric Blake has been through here and commented
on the interface itself.

> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
>  include/block/dirty-bitmap.h |  3 ++-
>  include/qemu/hbitmap.h       | 10 ++++++++--
>  block/backup.c               |  2 +-
>  block/dirty-bitmap.c         |  5 +++--
>  nbd/server.c                 |  2 +-
>  tests/test-hbitmap.c         |  2 +-
>  util/hbitmap.c               | 25 ++++++++++++++++++++-----
>  7 files changed, 36 insertions(+), 13 deletions(-)
> 
> diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
> index 259bd27c40..27f5299c4e 100644
> --- a/include/block/dirty-bitmap.h
> +++ b/include/block/dirty-bitmap.h
> @@ -98,7 +98,8 @@ bool bdrv_has_changed_persistent_bitmaps(BlockDriverState 
> *bs);
>  BdrvDirtyBitmap *bdrv_dirty_bitmap_next(BlockDriverState *bs,
>                                          BdrvDirtyBitmap *bitmap);
>  char *bdrv_dirty_bitmap_sha256(const BdrvDirtyBitmap *bitmap, Error **errp);
> -int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t start);
> +int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t start,
> +                                    int64_t end);
>  BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap_locked(BlockDriverState *bs,
>                                                    BdrvDirtyBitmap *bitmap,
>                                                    Error **errp);
> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
> index ddca52c48e..fe4dfde27a 100644
> --- a/include/qemu/hbitmap.h
> +++ b/include/qemu/hbitmap.h
> @@ -295,10 +295,16 @@ unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi);
>  /* hbitmap_next_zero:
>   * @hb: The HBitmap to operate on
>   * @start: The bit to start from.
> + * @end: End of range to search in. If @end is -1, search up to the bitmap
> + *       end.
>   *
> - * Find next not dirty bit.
> + * Find next not dirty bit within range address@hidden, @end), or from
> + * @start to the bitmap end if @end is -1. If not found, return -1.
> + *
> + * @end may be greater than original bitmap size, in this case, search up to

"original" bitmap size? I think that's just an implementation detail, we
can drop 'original' here, yes?

> + * the bitmap end.
>   */
> -int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start);
> +int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start, int64_t end);
>  

The interface looks weird because we can define a 'start' that's beyond
the 'end'.

I realize that you need a signed integer for 'end' to signify EOF...
should we do a 'bytes' parameter instead? (Did you already do that in an
earlier version and we changed it?)

Well, it's not a big deal to me personally.

>  /* hbitmap_create_meta:
>   * Create a "meta" hbitmap to track dirtiness of the bits in this HBitmap.
> diff --git a/block/backup.c b/block/backup.c
> index 8630d32926..9bfd3f7189 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -458,7 +458,7 @@ static void 
> backup_incremental_init_copy_bitmap(BackupBlockJob *job)
>              break;
>          }
>  
> -        offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset);
> +        offset = bdrv_dirty_bitmap_next_zero(job->sync_bitmap, offset, -1);
>          if (offset == -1) {
>              hbitmap_set(job->copy_bitmap, cluster, end - cluster);
>              break;
> diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
> index c9b8a6fd52..037ae62726 100644
> --- a/block/dirty-bitmap.c
> +++ b/block/dirty-bitmap.c
> @@ -785,9 +785,10 @@ char *bdrv_dirty_bitmap_sha256(const BdrvDirtyBitmap 
> *bitmap, Error **errp)
>      return hbitmap_sha256(bitmap->bitmap, errp);
>  }
>  
> -int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset)
> +int64_t bdrv_dirty_bitmap_next_zero(BdrvDirtyBitmap *bitmap, uint64_t offset,
> +                                    int64_t end)
>  {
> -    return hbitmap_next_zero(bitmap->bitmap, offset);
> +    return hbitmap_next_zero(bitmap->bitmap, offset, end);
>  }
>  
>  void bdrv_merge_dirty_bitmap(BdrvDirtyBitmap *dest, const BdrvDirtyBitmap 
> *src,
> diff --git a/nbd/server.c b/nbd/server.c
> index ea5fe0eb33..07920d123b 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -1952,7 +1952,7 @@ static unsigned int bitmap_to_extents(BdrvDirtyBitmap 
> *bitmap, uint64_t offset,
>      assert(begin < overall_end && nb_extents);
>      while (begin < overall_end && i < nb_extents) {
>          if (dirty) {
> -            end = bdrv_dirty_bitmap_next_zero(bitmap, begin);
> +            end = bdrv_dirty_bitmap_next_zero(bitmap, begin, -1);
>          } else {
>              bdrv_set_dirty_iter(it, begin);
>              end = bdrv_dirty_iter_next(it);
> diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
> index 5e67ac1d3a..6b6a40bddd 100644
> --- a/tests/test-hbitmap.c
> +++ b/tests/test-hbitmap.c
> @@ -939,7 +939,7 @@ static void test_hbitmap_iter_and_reset(TestHBitmapData 
> *data,
>  
>  static void test_hbitmap_next_zero_check(TestHBitmapData *data, int64_t 
> start)
>  {
> -    int64_t ret1 = hbitmap_next_zero(data->hb, start);
> +    int64_t ret1 = hbitmap_next_zero(data->hb, start, -1);
>      int64_t ret2 = start;
>      for ( ; ret2 < data->size && hbitmap_get(data->hb, ret2); ret2++) {
>          ;
> diff --git a/util/hbitmap.c b/util/hbitmap.c
> index bcd304041a..1687372504 100644
> --- a/util/hbitmap.c
> +++ b/util/hbitmap.c
> @@ -53,6 +53,9 @@
>   */
>  
>  struct HBitmap {
> +    /* Size of the bitmap, as requested in hbitmap_alloc. */
> +    uint64_t orig_size;
> +
>      /* Number of total bits in the bottom level.  */
>      uint64_t size;
>  
> @@ -192,16 +195,26 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap 
> *hb, uint64_t first)
>      }
>  }
>  
> -int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start)
> +int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t start, int64_t end)
>  {
>      size_t pos = (start >> hb->granularity) >> BITS_PER_LEVEL;
>      unsigned long *last_lev = hb->levels[HBITMAP_LEVELS - 1];
> -    uint64_t sz = hb->sizes[HBITMAP_LEVELS - 1];
>      unsigned long cur = last_lev[pos];
> -    unsigned start_bit_offset =
> -            (start >> hb->granularity) & (BITS_PER_LONG - 1);
> +    unsigned start_bit_offset;
> +    uint64_t end_bit, sz;
>      int64_t res;
>  
> +    if (start >= hb->orig_size || (end != -1 && end <= start)) {
> +        return -1;
> +    }
> +
> +    end_bit = end == -1 ? hb->size : ((end - 1) >> hb->granularity) + 1;
> +    sz = (end_bit + BITS_PER_LONG - 1) >> BITS_PER_LEVEL;
> +
> +    /* There may be some zero bits in @cur before @start. We are not 
> interested
> +     * in them, let's set them.
> +     */
> +    start_bit_offset = (start >> hb->granularity) & (BITS_PER_LONG - 1);
>      cur |= (1UL << start_bit_offset) - 1;
>      assert((start >> hb->granularity) < hb->size);
>  
> @@ -218,7 +231,7 @@ int64_t hbitmap_next_zero(const HBitmap *hb, uint64_t 
> start)
>      }
>  
>      res = (pos << BITS_PER_LEVEL) + ctol(cur);
> -    if (res >= hb->size) {
> +    if (res >= end_bit) {
>          return -1;
>      }
>  
> @@ -652,6 +665,8 @@ HBitmap *hbitmap_alloc(uint64_t size, int granularity)
>      HBitmap *hb = g_new0(struct HBitmap, 1);
>      unsigned i;
>  
> +    hb->orig_size = size;
> +
>      assert(granularity >= 0 && granularity < 64);
>      size = (size + (1ULL << granularity) - 1) >> granularity;
>      assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));
> 

Despite my comments, I'm OK with or without changes.

Reviewed-by: John Snow <address@hidden>



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