Re: [PATCH v1 1/2] mm/sparse: add sparse_init_nid()

[Oscar Salvador]

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@xxxxxxxxxx>
> ---
>  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);

s/sprase/sparse ?

>  
>  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);
> +	}
> +
> +	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));
> +}

s/sprase/sparse ?

> 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)

s/sprase/sparse ?

> +{
> +	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;
> +
> +	usemap_longs = BITS_TO_LONGS(SECTION_BLOCKFLAGS_BITS);
> +	usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nid),
> +							  usemap_size() *
> +							  map_count);
> +	if (!usemap) {
> +		pr_err("%s: usemap allocation failed", __func__);
> +		goto failed;
> +	}
> +	map_base = sparse_populate_node(pnum_begin, pnum_end,
> +					map_count, nid);
> +	map_index = 0;
> +	for_each_present_section_nr(pnum_begin, pnum) {
> +		if (pnum >= pnum_end)
> +			break;
> +
> +		BUG_ON(map_index == map_count);
> +		map = sprase_populate_node_section(map_base, map_index,
> +						   pnum, nid);

s/sprase/sparse ?

> +		if (!map) {
> +			pr_err("%s: memory map backing failed. Some memory will not be available.",
> +			       __func__);
> +			pnum_begin = pnum;
> +			goto failed;
> +		}
> +		check_usemap_section_nr(nid, usemap);
> +		sparse_init_one_section(__nr_to_section(pnum), pnum, map,
> +					usemap);
> +		map_index++;
> +		usemap += usemap_longs;

Hi Pavel,

uhm, maybe I am mistaken, but should not this be:

usemap += usemap_size(); ?

usermap_size() = 32 bytes
while 
usemap_longs = 4 bytes

AFAIK, each section->pageblock_flags holds 4 words, each word covers 16 pageblocks.
So 16 * 4 = 64 pageblocks, and each pageblock is 512 pfns.
So 64 * 512 = 32768 (PAGES_PER_SECTION).

Am I wrong?

> +	}
> +	return;
> +failed:
> +	/* We failed to allocate, mark all the following pnums as not present */
> +	for_each_present_section_nr(pnum_begin, pnum) {
> +		if (pnum >= pnum_end)
> +			break;
> +		ms = __nr_to_section(pnum);
> +		ms->section_mem_map = 0;
> +	}
> +}
> +
>  /*
>   * Allocate the accumulated non-linear sections, allocate a mem_map
>   * for each and record the physical to section mapping.
> -- 
> 2.18.0
> 

-- 
Oscar Salvador
SUSE L3