linux-kernel - Re: [PATCH 2] mm/kvmalloc: do not call kmalloc for size > KMALLOC_MAX

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Message-ID: <20181101102405.GE23921@dhcp22.suse.cz>
Date:   Thu, 1 Nov 2018 11:24:05 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2] mm/kvmalloc: do not call kmalloc for size >
 KMALLOC_MAX_SIZE

On Thu 01-11-18 13:09:16, Konstantin Khlebnikov wrote:
> Allocations over KMALLOC_MAX_SIZE could be served only by vmalloc.

I would go on and say that allocations with sizes too large can actually
trigger a warning (once you have posted in the previous version outside
of the changelog area) because that might be interesting to people -
there are deployments to panic on warning and then a warning is much
more important.

> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/util.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mm/util.c b/mm/util.c
> index 8bf08b5b5760..f5f04fa22814 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -392,6 +392,9 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
>  	gfp_t kmalloc_flags = flags;
>  	void *ret;
>  
> +	if (size > KMALLOC_MAX_SIZE)
> +		goto fallback;
> +
>  	/*
>  	 * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
>  	 * so the given set of flags has to be compatible.
> @@ -422,6 +425,7 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
>  	if (ret || size <= PAGE_SIZE)
>  		return ret;
>  
> +fallback:
>  	return __vmalloc_node_flags_caller(size, node, flags,
>  			__builtin_return_address(0));
>  }
> 

-- 
Michal Hocko
SUSE Labs