Re: [PATCH RFC 5/5] non-mm: discourage the usage of __GFP_NOFAIL and encourage GFP_NOFAIL

Vlastimil Babka
2024-07-24T09:53:56Z

On 7/24/24 10:55 AM, Barry Song wrote:
> From: Barry Song <v-songbaohua@oppo.com>
>
> GFP_NOFAIL includes the meaning of block and direct reclamation, which
> is essential for a true no-fail allocation. We are gradually starting
> to enforce this block semantics to prevent the potential misuse of
> __GFP_NOFAIL in atomic contexts in the future.
>
> A typical example of incorrect usage is in VDPA, where GFP_ATOMIC
> and __GFP_NOFAIL are used together.
>
> [RFC]: This patch seems quite large; I don't mind splitting it into
> multiple patches for different subsystems after patches 1 ~ 4 have
> been applied.
>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
>
> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
> index fa01818c1972..29eaf8b84b52 100644
> --- a/arch/powerpc/sysdev/xive/common.c
> +++ b/arch/powerpc/sysdev/xive/common.c
> @@ -1146,7 +1146,7 @@ static int __init xive_init_ipis(void)
> if (!ipi_domain)
> goto out_free_fwnode;
>
> - xive_ipis = kcalloc(nr_node_ids, sizeof(*xive_ipis), GFP_KERNEL | __GFP_NOFAIL);
> + xive_ipis = kcalloc(nr_node_ids, sizeof(*xive_ipis), GFP_KERNEL | GFP_NOFAIL);

This (and others) doesn't look great. Normally there's just one GFP_MAIN
that combines several commonly used together flags internally, with possibly
some | __GFP_EXTRA addition for less common modifications. Now you're
combining two GFP_MAIN's and that's just confusing.

So if we want to go this way, you'd need e.g.

GFP_KERNEL_NOFAIL which is GFP_KERNEL | __GFP_NOFAIL

And probably also GFP_NOFS_NOFAIL and GFP_NOIO_NOFAIL (sigh).

> if (!xive_ipis)
> goto out_free_domain;