When a bitmap is removed, we can clean some space on the disk. The size of a cluster may be larger, so is the size of the bitmap that includes many clusters. Some bitmaps can be as large as tens of megabytes. The flag QCOW2_DISCARD_ALWAYS allows a call to the raw_co_pdiscard() that does the actual cleaning of the image on disk, while with the flag QCOW2_DISCARD_OTHER, a reference count of the cluster is updated only.
Signed-off-by: Andrey Shinkevich <[email protected]> --- v1: Discard old bitmap directories in QCOW2 image In the first version of the patch, any call to qcow2_free_clusters() in block/qcow2-bitmap.c was with the flag QCOW2_DISCARD_ALWAYS, even in the cases when the cleaned space is insignificant, particularly, in case of bitmap directories. Discussed in the email thread with the message ID <1549974951-731285-1-git-send-email-andrey.shinkev...@virtuozzo.com> block/qcow2-bitmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c index 3ee524d..162744e 100644 --- a/block/qcow2-bitmap.c +++ b/block/qcow2-bitmap.c @@ -202,7 +202,7 @@ static void clear_bitmap_table(BlockDriverState *bs, uint64_t *bitmap_table, continue; } - qcow2_free_clusters(bs, addr, s->cluster_size, QCOW2_DISCARD_OTHER); + qcow2_free_clusters(bs, addr, s->cluster_size, QCOW2_DISCARD_ALWAYS); bitmap_table[i] = 0; } } -- 1.8.3.1
