Re: [PATCH] mm: migrate: restore the nmask after successfully allocating on the target node

[Matthew Wilcox]

On Wed, Mar 26, 2025 at 11:12:18AM +0800, wangchuanguo wrote:
> If memory is successfully allocated on the target node and the
> function directly returns without value restore for nmask,
> non-first migration operations in migrate_pages() by again label
> may ignore the nmask settings, thereby allowing new memory
> allocations for migration on any node.

I have no opinion on whether this is the right thing to do or not, but
if it is:

> +++ b/mm/vmscan.c
> @@ -1026,8 +1026,10 @@ struct folio *alloc_migrate_folio(struct folio *src, unsigned long private)
>  	mtc->nmask = NULL;
>  	mtc->gfp_mask |= __GFP_THISNODE;
>  	dst = alloc_migration_target(src, (unsigned long)mtc);
> -	if (dst)
> +	if (dst) {
> +		mtc->nmask = allowed_mask;
>  		return dst;
> +	}
>  
>  	mtc->gfp_mask &= ~__GFP_THISNODE;
>  	mtc->nmask = allowed_mask;

this should be:

	dst = alloc_migration_target(src, (unsigned long)mtc);
+	mtc->nmask = allowed_mask;
	if (dst)
		return dst;

	mtc->gfp_mask &= ~__GFP_THISNODE;
-	mtc->nmask = allowed_mask;