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Re: [PATCH v3 07/10] block/dirty-bitmap: improve _next_dirty_area API
From: |
Max Reitz |
Subject: |
Re: [PATCH v3 07/10] block/dirty-bitmap: improve _next_dirty_area API |
Date: |
Mon, 20 Jan 2020 14:58:47 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 |
On 19.12.19 11:03, Vladimir Sementsov-Ogievskiy wrote:
> Firstly, _next_dirty_area is for scenarios when we may contiguously
> search for next dirty area inside some limited region, so it is more
> comfortable to specify "end" which should not be recalculated on each
> iteration.
>
> Secondly, let's add a possibility to limit resulting area size, not
> limiting searching area. This will be used in NBD code in further
> commit. (Note that now bdrv_dirty_bitmap_next_dirty_area is unused)
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> ---
> include/block/dirty-bitmap.h | 3 ++-
> include/qemu/hbitmap.h | 25 ++++++++++++---------
> block/dirty-bitmap.c | 6 +++--
> tests/test-hbitmap.c | 43 +++++++++++++++++++++++-------------
> util/hbitmap.c | 41 +++++++++++++++++++++-------------
> 5 files changed, 74 insertions(+), 44 deletions(-)
[...]
> /**
> diff --git a/tests/test-hbitmap.c b/tests/test-hbitmap.c
> index e3f1b3f361..d75e84a76a 100644
> --- a/tests/test-hbitmap.c
> +++ b/tests/test-hbitmap.c
> @@ -920,18 +920,19 @@ static void
> test_hbitmap_next_x_after_truncate(TestHBitmapData *data,
> test_hbitmap_next_x_check(data, 0);
> }
>
> -static void test_hbitmap_next_dirty_area_check(TestHBitmapData *data,
> - int64_t offset,
> - int64_t count)
> +static void test_hbitmap_next_dirty_area_check_limited(TestHBitmapData *data,
> + int64_t offset,
> + int64_t count,
> + int64_t max_dirty)
> {
> int64_t off1, off2;
> int64_t len1 = 0, len2;
> bool ret1, ret2;
> int64_t end;
>
> - off1 = offset;
> - len1 = count;
> - ret1 = hbitmap_next_dirty_area(data->hb, &off1, &len1);
> + ret1 = hbitmap_next_dirty_area(data->hb,
> + offset, count == INT64_MAX ? INT64_MAX : offset + count,
> max_dirty,
> + &off1, &len1);
>
> end = offset > data->size || data->size - offset < count ? data->size :
> offset +
> count;
> @@ -940,21 +941,25 @@ static void
> test_hbitmap_next_dirty_area_check(TestHBitmapData *data,
> ;
These empty statements look a bit weird to me. But they’re
pre-existing, obviously.
> }
>
> - for (len2 = 1; off2 + len2 < end && hbitmap_get(data->hb, off2 + len2);
> - len2++) {
> + for (len2 = 1; (off2 + len2 < end && len2 < max_dirty &&
> + hbitmap_get(data->hb, off2 + len2)); len2++)
> + {
> ;
> }
[...]
> diff --git a/util/hbitmap.c b/util/hbitmap.c
> index d23f4b9678..2a1661ec1d 100644
> --- a/util/hbitmap.c
> +++ b/util/hbitmap.c
> @@ -270,22 +270,34 @@ int64_t hbitmap_next_zero(const HBitmap *hb, int64_t
> start, int64_t count)
> return res;
> }
>
> -bool hbitmap_next_dirty_area(const HBitmap *hb, int64_t *start, int64_t
> *count)
> +bool hbitmap_next_dirty_area(const HBitmap *hb, int64_t start, int64_t end,
> + int64_t max_dirty_count,
> + int64_t *dirty_start, int64_t *dirty_count)
> {
> - int64_t area_start, area_end;
> + int64_t next_zero;
>
> - area_start = hbitmap_next_dirty(hb, *start, *count);
> - if (area_start < 0) {
> + assert(start >= 0 && end >= 0 && max_dirty_count > 0);
> +
> + if (start >= hb->orig_size || end <= start) {
> + return false;
> + }
> +
> + end = MIN(end, hb->orig_size);
You could put this assignment before the if () and then drop the “start”
check from the condition. (But that’s mostly me itching to do
optimizations. I don’t think it’d make the code easier to read.)
[...]
> @@ -844,13 +856,12 @@ static void hbitmap_sparse_merge(HBitmap *dst, const
> HBitmap *src)
> int64_t offset = 0;
> int64_t count = src->orig_size;
These initializations are now unnecessary. I’d drop them because I find
at least the one for @count a tiny bit confusing now. (Because as a
reader, I’d wonder where this value is used.)
With that done (or maybe not because you disagree):
Reviewed-by: Max Reitz <address@hidden>
>
> - while (hbitmap_next_dirty_area(src, &offset, &count)) {
> + for (offset = 0;
> + hbitmap_next_dirty_area(src, offset, src->orig_size, INT64_MAX,
> + &offset, &count);
> + offset += count)
> + {
> hbitmap_set(dst, offset, count);
> - offset += count;
> - if (offset >= src->orig_size) {
> - break;
> - }
> - count = src->orig_size - offset;
> }
> }
>
>
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