Re: [PATCH v3 06/16] mm/page_alloc: relax GFP WARN in nolock allocs

[Vlastimil Babka (SUSE)]

On 6/29/26 15:11, Brendan Jackman wrote:
> This WARN forbids setting other flags than __GFP_ACCOUNT but we
> unconditionally set the ones in gfp_nolock so they are certainly fine
> for the caller to set.
> 
> There are other GFP flags that are almost certainly fine to set here;
> Willy noted GFP_HIGHMEM, GFP_DMA, GFP_MOVABLE and GFP_HARDWALL. But,
> nolock allocation is rather special, so be conservative to try and
> ensure we have a chance to think carefully before nontrivial new
> usecases arise.
> 
> Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/linux-mm/ajS96fWbG4dzP3u3@xxxxxxxxxxxxxxxxxxxx/
> Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>

> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8d409d075e3e9..9cb3f1665b41b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5355,7 +5355,8 @@ struct page *__alloc_frozen_pages_noprof(gfp_t gfp, unsigned int order,
>  		return NULL;
>  
>  	if (alloc_flags & ALLOC_NOLOCK) {
> -		VM_WARN_ON_ONCE(gfp & ~__GFP_ACCOUNT);
> +		/* Certain other flags could be supported later if needed. */
> +		VM_WARN_ON_ONCE(gfp & ~(__GFP_ACCOUNT | gfp_nolock));
>  		if (!alloc_trylock_allowed())
>  			return NULL;
>  		gfp |= gfp_nolock;
>