Re: [PATCH] ocfs2: fix cached cluster count after suballocator reclaim

[Heming Zhao]

Hello Matthias,

Could you share your test case, I want to reproduce the issue and verify the
fix.

Thanks,
Heming
On Wed, Aug 05, 2026 at 03:08:37PM +0800, Matthias Goergens wrote:
> When reclaiming a suballocator block group, first reduce the on-disk
> cluster count by cl_cpg.  The current code then subtracts that new count
> from the old cached count.
> 
> For an allocator with N groups, that leaves the cache at
> 
>     N * cl_cpg - (N - 1) * cl_cpg = cl_cpg
> 
> regardless of N.  This happens to be correct when reclaiming from two
> groups, but undercounts the clusters from three groups onwards.  The
> incorrect cache value is also used immediately to update i_blocks.
> 
> Assign the updated on-disk count to the cache, matching the allocation and
> inode refresh paths.
> 
> In a QEMU test using a clean 256 MiB OCFS2 image and a 10,000-file
> create/delete workload, the first buggy reclaim left the on-disk and cached
> counts at 2048 and 512 clusters respectively; later reclaims underflowed
> the cache.  With this change, the cache matched the on-disk count across
> all four reclaims: 2048, 1536, 1024, and 512 clusters.
> 
> Fixes: 4a54331616b3 ("ocfs2: give ocfs2 the ability to reclaim suballocator free bg")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Matthias Goergens <matthias.goergens@xxxxxxxxx>
> ---
>  fs/ocfs2/suballoc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> index a4a2b87a45fe3..20c3aec6b9873 100644
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> @@ -2759,7 +2759,7 @@ static int _ocfs2_reclaim_suballoc_to_main(handle_t *handle,
>  	fe->i_clusters = cpu_to_le32(tmp_used - le16_to_cpu(cl->cl_cpg));
>  
>  	spin_lock(&OCFS2_I(alloc_inode)->ip_lock);
> -	OCFS2_I(alloc_inode)->ip_clusters -= le32_to_cpu(fe->i_clusters);
> +	OCFS2_I(alloc_inode)->ip_clusters = le32_to_cpu(fe->i_clusters);
>  	fe->i_size = cpu_to_le64(ocfs2_clusters_to_bytes(alloc_inode->i_sb,
>  					     le32_to_cpu(fe->i_clusters)));
>  	spin_unlock(&OCFS2_I(alloc_inode)->ip_lock);
> -- 
> 2.55.0
>