Re: [Qemu-devel] [2.4 PATCH v3 15/19] block: Resize bitmaps on bdrv_truncate

[John Snow <jsnow@redhat.com>]

On 03/17/2015 09:50 AM, Max Reitz wrote:
> On 2015-03-13 at 14:30, John Snow wrote:
>> Signed-off-by: John Snow <jsnow@redhat.com>
>> ---
>>   block.c                | 18 +++++++++++++++++
>>   include/qemu/hbitmap.h | 10 ++++++++++
>>   util/hbitmap.c         | 52
>> ++++++++++++++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 80 insertions(+)
>>
>> diff --git a/block.c b/block.c
>> index 1eee394..f40b014 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -113,6 +113,7 @@ static void bdrv_set_dirty(BlockDriverState *bs,
>> int64_t cur_sector,
>>                              int nr_sectors);
>>   static void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector,
>>                                int nr_sectors);
>> +static void bdrv_dirty_bitmap_truncate(BlockDriverState *bs);
>>   /* If non-zero, use only whitelisted block drivers */
>>   static int use_bdrv_whitelist;
>> @@ -3543,6 +3544,7 @@ int bdrv_truncate(BlockDriverState *bs, int64_t
>> offset)
>>       ret = drv->bdrv_truncate(bs, offset);
>>       if (ret == 0) {
>>           ret = refresh_total_sectors(bs, offset >> BDRV_SECTOR_BITS);
>> +        bdrv_dirty_bitmap_truncate(bs);
>>           if (bs->blk) {
>>               blk_dev_resize_cb(bs->blk);
>>           }
>> @@ -5562,6 +5564,22 @@ BdrvDirtyBitmap
>> *bdrv_reclaim_dirty_bitmap(BlockDriverState *bs,
>>       return parent;
>>   }
>> +/**
>> + * Truncates _all_ bitmaps attached to a BDS.
>> + */
>> +static void bdrv_dirty_bitmap_truncate(BlockDriverState *bs)
>> +{
>> +    BdrvDirtyBitmap *bitmap;
>> +    uint64_t size = bdrv_nb_sectors(bs);
>> +
>> +    QLIST_FOREACH(bitmap, &bs->dirty_bitmaps, list) {
>> +        if (bdrv_dirty_bitmap_frozen(bitmap)) {
>> +            continue;
>> +        }
>> +        hbitmap_truncate(bitmap->bitmap, size);
>> +    }
>> +}
>> +
>>   void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap
>> *bitmap)
>>   {
>>       BdrvDirtyBitmap *bm, *next;
>> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
>> index c19c1cb..a75157e 100644
>> --- a/include/qemu/hbitmap.h
>> +++ b/include/qemu/hbitmap.h
>> @@ -65,6 +65,16 @@ struct HBitmapIter {
>>   HBitmap *hbitmap_alloc(uint64_t size, int granularity);
>>   /**
>> + * hbitmap_truncate:
>> + * @hb: The bitmap to change the size of.
>> + * @size: The number of elements to change the bitmap to accommodate.
>> + *
>> + * truncate or grow an existing bitmap to accommodate a new number of
>> elements.
>> + * This may invalidate existing HBitmapIterators.
>> + */
>> +void hbitmap_truncate(HBitmap *hb, uint64_t size);
>> +
>> +/**
>>    * hbitmap_merge:
>>    * @a: The bitmap to store the result in.
>>    * @b: The bitmap to merge into @a.
>> diff --git a/util/hbitmap.c b/util/hbitmap.c
>> index ba11fd3..4505ef7 100644
>> --- a/util/hbitmap.c
>> +++ b/util/hbitmap.c
>> @@ -400,6 +400,58 @@ HBitmap *hbitmap_alloc(uint64_t size, int
>> granularity)
>>       return hb;
>>   }
>> +void hbitmap_truncate(HBitmap *hb, uint64_t size)
>> +{
>> +    bool shrink;
>> +    unsigned i;
>> +    uint64_t num_elements = size;
>> +    uint64_t old;
>> +
>> +    /* Size comes in as logical elements, adjust for granularity. */
>> +    size = (size + (1ULL << hb->granularity) - 1) >> hb->granularity;
>> +    assert(size <= ((uint64_t)1 << HBITMAP_LOG_MAX_SIZE));
>> +    shrink = size < hb->size;
>> +
>> +    /* bit sizes are identical; nothing to do. */
>> +    if (size == hb->size) {
>> +        return;
>> +    }
>> +
>> +    /* If we're losing bits, let's clear those bits before we
>> invalidate all of
>> +     * our invariants. This helps keep the bitcount consistent, and
>> will prevent
>> +     * us from carrying around garbage bits beyond the end of the map.
>> +     *
>> +     * Because clearing bits past the end of map might reset bits we
>> care about
>> +     * within the array, record the current value of the last bit
>> we're keeping.
>> +     */
>> +    if (shrink) {
>> +        bool set = hbitmap_get(hb, num_elements - 1);
>> +        uint64_t fix_count = (hb->size << hb->granularity) -
>> num_elements;
>> +
>> +        assert(fix_count);
>> +        hbitmap_reset(hb, num_elements, fix_count);
>> +        if (set) {
>> +            hbitmap_set(hb, num_elements - 1, 1);
>> +        }
>> +    }
>> +
>> +    hb->size = size;
>> +    for (i = HBITMAP_LEVELS; i-- > 0; ) {
>> +        size = MAX(BITS_TO_LONGS(size), 1);
>
> Shouldn't this be "size = MAX(BITS_TO_LONGS(size) >> BITS_PER_LEVEL, 1);"?
>

I don't think so;

BITS_TO_LONGS(X) replaces the original construct:
(size + BITS_PER_LONG - 1) >> BITS_PER_LEVEL
which takes a size, adds <31|63> and then divides by <32|64>.

BITS_TO_LONGS performs DIV_ROUND_UP(nr, <32|64>), which will do 
effectively the same thing. (Actually, a little less efficiently, but I 
found this macro was nicer to read.)

>> +        if (hb->sizes[i] == size) {
>> +            break;
>> +        }
>> +        old = hb->sizes[i];
>> +        hb->sizes[i] = size;
>> +        hb->levels[i] = g_realloc(hb->levels[i], size *
>> sizeof(unsigned long));
>
> Any specific reason you got rid of the g_realloc_n()?
>

Not available in glib 2.12 (or 2.22.)

> Apart from these, the changes to v2 look good.
>
> Max
>
>> +        if (!shrink) {
>> +            memset(&hb->levels[i][old], 0x00,
>> +                   (size - old) * sizeof(*hb->levels[i]));
>> +        }
>> +    }
>> +}
>> +
>> +
>>   /**
>>    * Given HBitmaps A and B, let A := A (BITOR) B.
>>    * Bitmap B will not be modified.
>
>