Re: [PATCH] mm/page_alloc.c: avoid inheritting current's flags when invoked in interrupt

[Andrew Morton]

On Tue, 15 Sep 2020 15:56:35 +0800 <yanfei.xu@xxxxxxxxxxxxx> wrote:

> From: Yanfei Xu <yanfei.xu@xxxxxxxxxxxxx>
> 
> alloc_mask shouldn't inherit the current task's flags when
> __alloc_pages_nodemask is invoked in interrupt.
> 
> ...
>
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4889,7 +4889,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, int preferred_nid,
>  	 * from a particular context which has been marked by
>  	 * memalloc_no{fs,io}_{save,restore}.
>  	 */
> -	alloc_mask = current_gfp_context(gfp_mask);
> +	if (!in_interrupt())
> +		alloc_mask = current_gfp_context(gfp_mask);
>  	ac.spread_dirty_pages = false;
>  
>  	/*

hm, yes, and perhaps other callsites in page_alloc.c.

I assume this doesn't actually make any runtime difference?  Because
gfp_mask in interrupt contexts isn't going to have __GFP_IO or __GFP_FS
anyway.