linux-kernel - Re: [PATCH V2 3/6] mm/sparse: move mem_sections allocation out of memory

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Date:   Mon, 31 May 2021 14:39:02 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     Dong Aisheng <aisheng.dong@....com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dongas86@...il.com" <dongas86@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH V2 3/6] mm/sparse: move mem_sections allocation out of
 memory_present()

* Dong Aisheng <aisheng.dong@....com> [210531 05:20]:
> The only path to call memory_present() is from memblocks_present().
> The struct mem_section **mem_section only needs to be initialized once,
> so no need put the initialization/allocation code in memory_present()
> which will be called multiple times for each section.
> 
> After moving, the 'unlikely' condition statement becomes to be
> meaningless as it's only initialized one time, so dropped as well.
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Mike Rapoport <rppt@...nel.org>
> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> ---
> ChangeLog:
> v1->v2:
>  * split into a helper function and called directly from sparse_init
> ---
>  mm/sparse.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 408b737e168e..d02ee6bb7cbc 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -60,6 +60,18 @@ static inline void set_section_nid(unsigned long section_nr, int nid)
>  #endif
>  
>  #ifdef CONFIG_SPARSEMEM_EXTREME
> +static void __init sparse_alloc_section_roots(void)
> +{
> +	unsigned long size, align;
> +
> +	size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> +	align = 1 << (INTERNODE_CACHE_SHIFT);
> +	mem_section = memblock_alloc(size, align);
> +	if (!mem_section)
> +		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
> +		      __func__, size, align);
> +}
> +
>  static noinline struct mem_section __ref *sparse_index_alloc(int nid)
>  {
>  	struct mem_section *section = NULL;
> @@ -107,6 +119,8 @@ static inline int sparse_index_init(unsigned long section_nr, int nid)
>  {
>  	return 0;
>  }
> +
> +static inline void sparse_alloc_section_roots(void) {}
>  #endif
>  
>  #ifdef CONFIG_SPARSEMEM_EXTREME
> @@ -254,19 +268,6 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
>  {
>  	unsigned long pfn;
>  
> -#ifdef CONFIG_SPARSEMEM_EXTREME
> -	if (unlikely(!mem_section)) {
> -		unsigned long size, align;
> -
> -		size = sizeof(struct mem_section *) * NR_SECTION_ROOTS;
> -		align = 1 << (INTERNODE_CACHE_SHIFT);
> -		mem_section = memblock_alloc(size, align);
> -		if (!mem_section)
> -			panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
> -			      __func__, size, align);
> -	}
> -#endif
> -
>  	start &= PAGE_SECTION_MASK;
>  	mminit_validate_memmodel_limits(&start, &end);
>  	for (pfn = start; pfn < end; pfn += PAGES_PER_SECTION) {
> @@ -582,6 +583,8 @@ void __init sparse_init(void)
>  	unsigned long pnum_end, pnum_begin, map_count = 1;
>  	int nid_begin;
>  
> +	sparse_alloc_section_roots();

nit: The newline below is unnecessary

> +
>  	memblocks_present();
>  
>  	pnum_begin = first_present_section_nr();
> -- 
> 2.25.1
> 
>