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

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Message-ID: <Z-N0ep6Vv6D9QRik@casper.infradead.org>
Date: Wed, 26 Mar 2025 03:28:58 +0000
From: Matthew Wilcox <willy@...radead.org>
To: wangchuanguo <wangchuanguo@...pur.com>
Cc: akpm@...ux-foundation.org, mhiramat@...nel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: migrate: restore the nmask after successfully
 allocating on the  target node

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;