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Date:   Mon, 2 Jul 2018 09:29:33 +0800
From:   Baoquan He <bhe@redhat.com>
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,
        gregkh@linuxfoundation.org, vbabka@suse.cz,
        richard.weiyang@gmail.com, dave.hansen@intel.com,
        rientjes@google.com, mingo@kernel.org, osalvador@techadventures.net
Subject: Re: [PATCH v2 1/2] mm/sparse: add sparse_init_nid()
Message-ID: <20180702012933.GH3223@MiWiFi-R3L-srv>
References: <20180630030944.9335-1-pasha.tatashin@oracle.com>
 <20180630030944.9335-2-pasha.tatashin@oracle.com>
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On 06/29/18 at 11:09pm, 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.

These two temporary buffers are large when CONFIG_X86_5LEVEL is enabled.
Otherwise it's OK.

> 
> 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>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> ---
>  include/linux/mm.h  |  8 ++++
>  mm/sparse-vmemmap.c | 49 ++++++++++++++++++++++++
>  mm/sparse.c         | 91 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 148 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index a0fbb9ffe380..85530fdfb1f2 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 * sparse_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..b3e325962306 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 sparse_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..c18d92b8ab9b 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 sparse_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 sparse_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 +557,60 @@ 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;
> +
> +	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 = sparse_populate_node_section(map_base, map_index,
> +						   pnum, nid);
> +		if (!map) {
> +			pr_err("%s: memory map backing failed. Some memory will not be available.",
> +			       __func__);
> +			pnum_begin = pnum;
> +			goto failed;

If one memmap is unavailable, do we need to jump to 'failed' to mark all
sections of the node as not present? E.g the last section of one node
failed to populate memmap?


> +		}
> +		check_usemap_section_nr(nid, usemap);
> +		sparse_init_one_section(__nr_to_section(pnum), pnum, map,
> +					usemap);
> +		map_index++;
> +		usemap += usemap_longs;
> +	}
> +	return;
> +failed:
> +	/* We failed to allocate, mark all the following pnums as not present */
> +	for_each_present_section_nr(pnum_begin, pnum) {
> +		struct mem_section *ms;
> +
> +		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
>