linux-kernel - Re: [PATCH 3/9] rhashtable: simplify a strange allocation pattern

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Date:   Mon, 30 Jan 2017 15:04:43 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     David Rientjes <rientjes@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        Tom Herbert <tom@...bertland.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 3/9] rhashtable: simplify a strange allocation pattern

On 01/30/2017 10:49 AM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
>
> alloc_bucket_locks allocation pattern is quite unusual. We are
> preferring vmalloc when CONFIG_NUMA is enabled. The rationale is that
> vmalloc will respect the memory policy of the current process and so the
> backing memory will get distributed over multiple nodes if the requester
> is configured properly. At least that is the intention, in reality
> rhastable is shrunk and expanded from a kernel worker so no mempolicy
> can be assumed.
>
> Let's just simplify the code and use kvmalloc helper, which is a
> transparent way to use kmalloc with vmalloc fallback, if the caller
> is allowed to block and use the flag otherwise.
>
> Cc: Tom Herbert <tom@...bertland.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  lib/rhashtable.c | 13 +++----------
>  1 file changed, 3 insertions(+), 10 deletions(-)
>
> diff --git a/lib/rhashtable.c b/lib/rhashtable.c
> index 32d0ad058380..1a487ea70829 100644
> --- a/lib/rhashtable.c
> +++ b/lib/rhashtable.c
> @@ -77,16 +77,9 @@ static int alloc_bucket_locks(struct rhashtable *ht, struct bucket_table *tbl,
>  	size = min_t(unsigned int, size, tbl->size >> 1);
>
>  	if (sizeof(spinlock_t) != 0) {
> -		tbl->locks = NULL;
> -#ifdef CONFIG_NUMA
> -		if (size * sizeof(spinlock_t) > PAGE_SIZE &&
> -		    gfp == GFP_KERNEL)
> -			tbl->locks = vmalloc(size * sizeof(spinlock_t));
> -#endif
> -		if (gfp != GFP_KERNEL)
> -			gfp |= __GFP_NOWARN | __GFP_NORETRY;
> -
> -		if (!tbl->locks)
> +		if (gfpflags_allow_blocking(gfp))
> +			tbl->locks = kvmalloc(size * sizeof(spinlock_t), gfp);
> +		else
>  			tbl->locks = kmalloc_array(size, sizeof(spinlock_t),
>  						   gfp);
>  		if (!tbl->locks)
>