Re: [PATCH v5 12/12] mm, swap: merge zeromap into swap table

[Andrew Morton]

On Sun, 17 May 2026 23:39:51 +0800 Kairui Song via B4 Relay <devnull+kasong.tencent.com@xxxxxxxxxx> wrote:

> From: Kairui Song <kasong@xxxxxxxxxxx>
> 
> By allocating one additional bit in the swap table entry's flags field
> alongside the count, we can store the zeromap inline
> 
> For 64 bit systems, zeromap will store in the swap table, avoiding zeromap
> allocation. It reduces the allocated memory. That is the happy path.
> 
> For certain 32-bit archs, there might not be enough bits in the swap
> table to contain both PFN and flags. Therefore, conditionally let each
> cluster have a zeromap field at build time, and use that instead.
> If the swapfile cluster is not fully used, it will still save memory for
> zeromap. The empty cluster does not allocate a zeromap. In the worst case,
> all cluster are fully populated. We will use memory similar to the
> previous zeromap implementation.
> 
> A few macros were moved to different headers for build time struct
> definition.
> 
> ...
>
> @@ -469,13 +474,21 @@ static int swap_cluster_alloc_table(struct swap_cluster_info *ci, gfp_t gfp)
>  		VM_WARN_ON_ONCE(ci->memcg_table);
>  		ci->memcg_table = kzalloc_obj(*ci->memcg_table, gfp);
>  		if (!ci->memcg_table)
> -			ret = -ENOMEM;
> +			goto err_free;
>  	}
>  #endif
> -	if (ret)
> -		swap_cluster_free_table(ci);
>  
> -	return ret;
> +#if !SWAP_TABLE_HAS_ZEROFLAG
> +	VM_WARN_ON_ONCE(ci->zero_bitmap);
> +	ci->zero_bitmap = bitmap_zalloc(SWAPFILE_CLUSTER, gfp);
> +	if (!ci->zero_bitmap)
> +		goto err_free;
> +#endif
> +	return 0;
> +
> +err_free:
> +	swap_cluster_free_table(ci);
> +	return -ENOMEM;
>  }

My m68k defconfig warned.  I'll do the below, which looks good enough. 
Please check.

Perhaps a custom guard() handler would clean things up here.


From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: mm-swap-merge-zeromap-into-swap-table-fix-2
Date: Thu May 21 06:39:20 PM PDT 2026

mm/swapfile.c: In function 'swap_cluster_alloc_table':
mm/swapfile.c:488:1: warning: label 'err_free' defined but not used [-Wunused-label]
  488 | err_free:
      | ^~~~~~~~

Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Barry Song <baohua@xxxxxxxxxx>
Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Cc: Lorenzo Stoakes <ljs@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeel.butt@xxxxxxxxx>
Cc: Youngjun Park <youngjun.park@xxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/swapfile.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- a/mm/swapfile.c~mm-swap-merge-zeromap-into-swap-table-fix-2
+++ a/mm/swapfile.c
@@ -472,22 +472,22 @@ static int swap_cluster_alloc_table(stru
 	if (!mem_cgroup_disabled()) {
 		VM_WARN_ON_ONCE(ci->memcg_table);
 		ci->memcg_table = kzalloc_obj(*ci->memcg_table, gfp);
-		if (!ci->memcg_table)
-			goto err_free;
+		if (!ci->memcg_table) {
+			swap_cluster_free_table(ci);
+			return -ENOMEM;
+		}
 	}
 #endif
 
 #if !SWAP_TABLE_HAS_ZEROFLAG
 	VM_WARN_ON_ONCE(ci->zero_bitmap);
 	ci->zero_bitmap = bitmap_zalloc(SWAPFILE_CLUSTER, gfp);
-	if (!ci->zero_bitmap)
-		goto err_free;
+	if (!ci->zero_bitmap) {
+		swap_cluster_free_table(ci);
+		return -ENOMEM;
+	}
 #endif
 	return 0;
-
-err_free:
-	swap_cluster_free_table(ci);
-	return -ENOMEM;
 }
 
 /*
_