linux-kernel - Re: [PATCH 1/2] mm/memblock: prepare a capability to support memblock near alloc

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Message-ID: <20161025132338.GA31239@dhcp22.suse.cz>
Date:   Tue, 25 Oct 2016 15:23:38 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>, Zefan Li <lizefan@...wei.com>,
        Xinwei Hu <huxinwei@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>
Subject: Re: [PATCH 1/2] mm/memblock: prepare a capability to support
 memblock near alloc

On Tue 25-10-16 10:59:17, Zhen Lei wrote:
> If HAVE_MEMORYLESS_NODES is selected, and some memoryless numa nodes are
> actually exist. The percpu variable areas and numa control blocks of that
> memoryless numa nodes need to be allocated from the nearest available
> node to improve performance.
> 
> Although memblock_alloc_try_nid and memblock_virt_alloc_try_nid try the
> specified nid at the first time, but if that allocation failed it will
> directly drop to use NUMA_NO_NODE. This mean any nodes maybe possible at
> the second time.
> 
> To compatible the above old scene, I use a marco node_distance_ready to
> control it. By default, the marco node_distance_ready is not defined in
> any platforms, the above mentioned functions will work as normal as
> before. Otherwise, they will try the nearest node first.

I am sorry but it is absolutely unclear to me _what_ is the motivation
of the patch. Is this a performance optimization, correctness issue or
something else? Could you please restate what is the problem, why do you
think it has to be fixed at memblock layer and describe what the actual
fix is please?

>From a quick glance you are trying to bend over the memblock API for
something that should be handled on a different layer.

> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> ---
>  mm/memblock.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 65 insertions(+), 11 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 7608bc3..556bbd2 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1213,9 +1213,71 @@ phys_addr_t __init memblock_alloc(phys_addr_t size, phys_addr_t align)
>  	return memblock_alloc_base(size, align, MEMBLOCK_ALLOC_ACCESSIBLE);
>  }
> 
> +#ifndef node_distance_ready
> +#define node_distance_ready()		0
> +#endif
> +
> +static phys_addr_t __init memblock_alloc_near_nid(phys_addr_t size,
> +					phys_addr_t align, phys_addr_t start,
> +					phys_addr_t end, int nid, ulong flags,
> +					int alloc_func_type)
> +{
> +	int nnid, round = 0;
> +	u64 pa;
> +	DECLARE_BITMAP(nodes_map, MAX_NUMNODES);
> +
> +	bitmap_zero(nodes_map, MAX_NUMNODES);
> +
> +again:
> +	/*
> +	 * There are total 4 cases:
> +	 * <nid == NUMA_NO_NODE>
> +	 *   1)2) node_distance_ready || !node_distance_ready
> +	 *	Round 1, nnid = nid = NUMA_NO_NODE;
> +	 * <nid != NUMA_NO_NODE>
> +	 *   3) !node_distance_ready
> +	 *	Round 1, nnid = nid;
> +	 *    ::Round 2, currently only applicable for alloc_func_type = <0>
> +	 *	Round 2, nnid = NUMA_NO_NODE;
> +	 *   4) node_distance_ready
> +	 *	Round 1, LOCAL_DISTANCE, nnid = nid;
> +	 *	Round ?, nnid = nearest nid;
> +	 */
> +	if (!node_distance_ready() || (nid == NUMA_NO_NODE)) {
> +		nnid = (++round == 1) ? nid : NUMA_NO_NODE;
> +	} else {
> +		int i, distance = INT_MAX;
> +
> +		for_each_clear_bit(i, nodes_map, MAX_NUMNODES)
> +			if (node_distance(nid, i) < distance) {
> +				nnid = i;
> +				distance = node_distance(nid, i);
> +			}
> +	}
> +
> +	switch (alloc_func_type) {
> +	case 0:
> +		pa = memblock_find_in_range_node(size, align, start, end, nnid, flags);
> +		break;
> +
> +	case 1:
> +	default:
> +		pa = memblock_alloc_nid(size, align, nnid);
> +		if (!node_distance_ready())
> +			return pa;
> +	}
> +
> +	if (!pa && (nnid != NUMA_NO_NODE)) {
> +		bitmap_set(nodes_map, nnid, 1);
> +		goto again;
> +	}
> +
> +	return pa;
> +}
> +
>  phys_addr_t __init memblock_alloc_try_nid(phys_addr_t size, phys_addr_t align, int nid)
>  {
> -	phys_addr_t res = memblock_alloc_nid(size, align, nid);
> +	phys_addr_t res = memblock_alloc_near_nid(size, align, 0, 0, nid, 0, 1);
> 
>  	if (res)
>  		return res;
> @@ -1276,19 +1338,11 @@ static void * __init memblock_virt_alloc_internal(
>  		max_addr = memblock.current_limit;
> 
>  again:
> -	alloc = memblock_find_in_range_node(size, align, min_addr, max_addr,
> -					    nid, flags);
> +	alloc = memblock_alloc_near_nid(size, align, min_addr, max_addr,
> +					    nid, flags, 0);
>  	if (alloc)
>  		goto done;
> 
> -	if (nid != NUMA_NO_NODE) {
> -		alloc = memblock_find_in_range_node(size, align, min_addr,
> -						    max_addr, NUMA_NO_NODE,
> -						    flags);
> -		if (alloc)
> -			goto done;
> -	}
> -
>  	if (min_addr) {
>  		min_addr = 0;
>  		goto again;
> --
> 2.5.0
> 

-- 
Michal Hocko
SUSE Labs