Re: [PATCH v2] ocfs2: fix cached cluster count after suballocator reclaim

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 8/5/26 7:39 PM, 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 (fe->i_clusters) from the old cached count
> (OCFS2_I(alloc_inode)->ip_clusters).
> 
> For an allocator with N block groups, that leaves the cache at
> 
>     N * cl_cpg - (N * cl_cpg - cl_cpg) = cl_cpg
> 
> i.e. ip_clusters -= (fe->i_clusters - cl_cpg) leaves ip_clusters equal
> to cl_cpg regardless of N.  This happens to be correct when reclaiming
> from two block groups, but undercounts the clusters from three block
> 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
> (fe->i_clusters) and cached (ip_clusters) 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@vger.kernel.org
> Signed-off-by: Matthias Goergens <matthias.goergens@gmail.com>

Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>

> ---
> 
> v2: commit-log wording revisions suggested by Heming Zhao; code unchanged.
>  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);