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Date:   Fri, 29 Jun 2018 16:35:27 +0200
From:   Oscar Salvador <osalvador@techadventures.net>
To:     Pavel Tatashin <pasha.tatashin@oracle.com>
Cc:     steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        kirill.shutemov@linux.intel.com, mhocko@suse.com,
        linux-mm@kvack.org, dan.j.williams@intel.com, jack@suse.cz,
        jglisse@redhat.com, jrdr.linux@gmail.com, bhe@redhat.com,
        gregkh@linuxfoundation.org, vbabka@suse.cz,
        richard.weiyang@gmail.com, dave.hansen@intel.com,
        rientjes@google.com, mingo@kernel.org
Subject: Re: [PATCH v1 1/2] mm/sparse: add sparse_init_nid()
Message-ID: <20180629143527.GA23545@techadventures.net>
References: <20180628173010.23849-1-pasha.tatashin@oracle.com>
 <20180628173010.23849-2-pasha.tatashin@oracle.com>
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On Thu, Jun 28, 2018 at 01:30:09PM -0400, Pavel Tatashin wrote:
> sparse_init() requires to temporary allocate two large buffers:
> usemap_map and map_map. Baoquan He has identified that these buffers are so
> large that Linux is not bootable on small memory machines, such as a kdump
> boot.
> 
> Baoquan provided a fix, which reduces these sizes of these buffers, but it
> is much better to get rid of them entirely.
> 
> Add a new way to initialize sparse memory: sparse_init_nid(), which only
> operates within one memory node, and thus allocates memory either in large
> contiguous block or allocates section by section. This eliminates the need
> for use of temporary buffers.
> 
> For simplified bisecting and review, the new interface is going to be
> enabled as well as old code removed in the next patch.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
> ---
>  include/linux/mm.h  |  8 ++++
>  mm/sparse-vmemmap.c | 49 ++++++++++++++++++++++++
>  mm/sparse.c         | 90 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 147 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a0fbb9ffe380..ba200808dd5f 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -2651,6 +2651,14 @@ void sparse_mem_maps_populate_node(struct page **map_map,
>  				   unsigned long pnum_end,
>  				   unsigned long map_count,
>  				   int nodeid);
> +struct page * sparse_populate_node(unsigned long pnum_begin,
> +				   unsigned long pnum_end,
> +				   unsigned long map_count,
> +				   int nid);
> +struct page * sprase_populate_node_section(struct page *map_base,
> +				   unsigned long map_index,
> +				   unsigned long pnum,
> +				   int nid);
>  
>  struct page *sparse_mem_map_populate(unsigned long pnum, int nid,
>  		struct vmem_altmap *altmap);
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index e1a54ba411ec..4655503bdc66 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -311,3 +311,52 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
>  		vmemmap_buf_end = NULL;
>  	}
>  }
> +
> +struct page * __init sparse_populate_node(unsigned long pnum_begin,
> +					  unsigned long pnum_end,
> +					  unsigned long map_count,
> +					  int nid)
> +{
> +	unsigned long size = sizeof(struct page) * PAGES_PER_SECTION;
> +	unsigned long pnum, map_index = 0;
> +	void *vmemmap_buf_start;
> +
> +	size = ALIGN(size, PMD_SIZE) * map_count;
> +	vmemmap_buf_start = __earlyonly_bootmem_alloc(nid, size,
> +						      PMD_SIZE,
> +						      __pa(MAX_DMA_ADDRESS));
> +	if (vmemmap_buf_start) {
> +		vmemmap_buf = vmemmap_buf_start;
> +		vmemmap_buf_end = vmemmap_buf_start + size;
> +	}
> +
> +	for (pnum = pnum_begin; map_index < map_count; pnum++) {
> +		if (!present_section_nr(pnum))
> +			continue;
> +		if (!sparse_mem_map_populate(pnum, nid, NULL))
> +			break;
> +		map_index++;
> +		BUG_ON(pnum >= pnum_end);
> +	}

Besides the typos, I could not find anything wrong in the patch.
Only cosmetic:

Could not the loop above be converted to a for_each_present_section_nr() or would it be
less readable?

> +
> +	if (vmemmap_buf_start) {
> +		/* need to free left buf */
> +		memblock_free_early(__pa(vmemmap_buf),
> +				    vmemmap_buf_end - vmemmap_buf);
> +		vmemmap_buf = NULL;
> +		vmemmap_buf_end = NULL;
> +	}
> +	return pfn_to_page(section_nr_to_pfn(pnum_begin));
> +}
> +
> +/*
> + * Return map for pnum section. sparse_populate_node() has populated memory map
> + * in this node, we simply do pnum to struct page conversion.
> + */
> +struct page * __init sprase_populate_node_section(struct page *map_base,
> +						  unsigned long map_index,
> +						  unsigned long pnum,
> +						  int nid)
> +{
> +	return pfn_to_page(section_nr_to_pfn(pnum));
> +}
> diff --git a/mm/sparse.c b/mm/sparse.c
> index d18e2697a781..60eaa2a4842a 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -456,6 +456,43 @@ void __init sparse_mem_maps_populate_node(struct page **map_map,
>  		       __func__);
>  	}
>  }
> +
> +static unsigned long section_map_size(void)
> +{
> +	return PAGE_ALIGN(sizeof(struct page) * PAGES_PER_SECTION);
> +}
> +
> +/*
> + * Try to allocate all struct pages for this node, if this fails, we will
> + * be allocating one section at a time in sprase_populate_node_section().
> + */
> +struct page * __init sparse_populate_node(unsigned long pnum_begin,
> +					  unsigned long pnum_end,
> +					  unsigned long map_count,
> +					  int nid)
> +{
> +	return memblock_virt_alloc_try_nid_raw(section_map_size() * map_count,
> +					       PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
> +					       BOOTMEM_ALLOC_ACCESSIBLE, nid);
> +}
> +
> +/*
> + * Return map for pnum section. map_base is not NULL if we could allocate map
> + * for this node together. Otherwise we allocate one section at a time.
> + * map_index is the index of pnum in this node counting only present sections.
> + */
> +struct page * __init sprase_populate_node_section(struct page *map_base,
> +						  unsigned long map_index,
> +						  unsigned long pnum,
> +						  int nid)
> +{
> +	if (map_base) {
> +		unsigned long offset = section_map_size() * map_index;
> +
> +		return (struct page *)((char *)map_base + offset);
> +	}
> +	return sparse_mem_map_populate(pnum, nid, NULL);
> +}
>  #endif /* !CONFIG_SPARSEMEM_VMEMMAP */
>  
>  static void __init sparse_early_mem_maps_alloc_node(void *data,
> @@ -520,6 +557,59 @@ static void __init alloc_usemap_and_memmap(void (*alloc_func)
>  						map_count, nodeid_begin);
>  }
>  
> +/*
> + * Initialize sparse on a specific node. The node spans [pnum_begin, pnum_end)
> + * And number of present sections in this node is map_count.
> + */
> +void __init sparse_init_nid(int nid, unsigned long pnum_begin,
> +				   unsigned long pnum_end,
> +				   unsigned long map_count)
> +{
> +	unsigned long pnum, usemap_longs, *usemap, map_index;
> +	struct page *map, *map_base;
> +	struct mem_section *ms;

What about moving "struct mem_section" into the second for_each_present_section_nr() loop.
It is only being used there.
And we could move "struct page *map" into the first loop as well.

But the patch looks good to me anyway.
Maybe I am missing something, but so far:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

-- 
Oscar Salvador
SUSE L3