Anatol Belski 57f67a543a block: qcow: Reuse relocated refcount block clusters ...

Metadata tables use relocate on write. The first modification after a
flush writes the table to a new cluster and frees the old one. The L2
path returns the old cluster to the free list, but the refcount block
path did not. QcowState::set_cluster_refcount set the dropped refcount
block cluster to refcount 0 yet never pushed it onto unref_clusters, so
it stayed committed on the host and was invisible to the allocator.
Every refcount block relocation stranded one cluster, and
get_new_cluster extended the file instead of reusing it.

Under a sync heavy workload each fsync that dirties a table relocates
it, so the physical footprint grew at roughly twice the live data
without bound. qemu-img check stayed clean because the refcounts are
correct, and a reopen, which rebuilds the free list from refcounts,
recovered the space.

Push the dropped refcount block cluster onto unref_clusters so the
running allocator reuses it, matching the L2 table path.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

2026-07-16 13:03:48 +00:00

..

src

block: qcow: Reuse relocated refcount block clusters

2026-07-16 13:03:48 +00:00

Cargo.toml

build(deps): bump the non-rust-vmm group across 2 directories with 13 updates

2026-07-10 00:53:35 +00:00