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From:   "NeilBrown" <neilb@suse.de>
To:     "Michal Hocko" <mhocko@kernel.org>
Cc:     linux-mm@kvack.org, "Dave Chinner" <david@fromorbit.com>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        "Christoph Hellwig" <hch@infradead.org>,
        "Uladzislau Rezki" <urezki@gmail.com>,
        linux-fsdevel@vger.kernel.org,
        "LKML" <linux-kernel@vger.kernel.org>,
        "Ilya Dryomov" <idryomov@gmail.com>,
        "Jeff Layton" <jlayton@kernel.org>,
        "Michal Hocko" <mhocko@suse.com>
Subject: Re: [PATCH 2/4] mm/vmalloc: add support for __GFP_NOFAIL
In-reply-to: <20211025150223.13621-3-mhocko@kernel.org>
References: <20211025150223.13621-1-mhocko@kernel.org>,
 <20211025150223.13621-3-mhocko@kernel.org>
Date:   Tue, 26 Oct 2021 09:59:36 +1100
Message-id: <163520277623.16092.15759069160856953654@noble.neil.brown.name>
Precedence: bulk

On Tue, 26 Oct 2021, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
>=20
> Dave Chinner has mentioned that some of the xfs code would benefit from
> kvmalloc support for __GFP_NOFAIL because they have allocations that
> cannot fail and they do not fit into a single page.
>=20
> The larg part of the vmalloc implementation already complies with the

*large*

> given gfp flags so there is no work for those to be done. The area
> and page table allocations are an exception to that. Implement a retry
> loop for those.
>=20
> Add a short sleep before retrying. 1 jiffy is a completely random
> timeout. Ideally the retry would wait for an explicit event - e.g.
> a change to the vmalloc space change if the failure was caused by
> the space fragmentation or depletion. But there are multiple different
> reasons to retry and this could become much more complex. Keep the retry
> simple for now and just sleep to prevent from hogging CPUs.
>=20
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  mm/vmalloc.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>=20
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index c6cc77d2f366..602649919a9d 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2941,8 +2941,12 @@ static void *__vmalloc_area_node(struct vm_struct *a=
rea, gfp_t gfp_mask,
>  	else if ((gfp_mask & (__GFP_FS | __GFP_IO)) =3D=3D 0)
>  		flags =3D memalloc_noio_save();
> =20
> -	ret =3D vmap_pages_range(addr, addr + size, prot, area->pages,
> +	do {
> +		ret =3D vmap_pages_range(addr, addr + size, prot, area->pages,
>  			page_shift);
> +		if (ret < 0)
> +			schedule_timeout_uninterruptible(1);
> +	} while ((gfp_mask & __GFP_NOFAIL) && (ret < 0));
> =20
>  	if ((gfp_mask & (__GFP_FS | __GFP_IO)) =3D=3D __GFP_IO)
>  		memalloc_nofs_restore(flags);
> @@ -3032,6 +3036,10 @@ void *__vmalloc_node_range(unsigned long size, unsig=
ned long align,
>  		warn_alloc(gfp_mask, NULL,
>  			"vmalloc error: size %lu, vm_struct allocation failed",
>  			real_size);
> +		if (gfp_mask & __GFP_NOFAIL) {
> +			schedule_timeout_uninterruptible(1);
> +			goto again;
> +		}

Shouldn't the retry happen *before* the warning?

NeilBrown


>  		goto fail;
>  	}
> =20
> --=20
> 2.30.2
>=20
>=20