Re: [PATCH v2 3/3] mm/sparse: Optimize memmap allocation during sparse_init()

[Baoquan He]

Hi Pankaj,

On 02/22/18 at 05:07am, Pankaj Gupta wrote:
> 
> Hi Baoquan,
> 
> > 
> > In sparse_init(), two temporary pointer arrays, usemap_map and map_map
> > are allocated with the size of NR_MEM_SECTIONS. They are used to store
> > each memory section's usemap and mem map if marked as present. With
> > the help of these two arrays, continuous memory chunk is allocated for
> > usemap and memmap for memory sections on one node. This avoids too many
> > memory fragmentations. Like below diagram, '1' indicates the present
> > memory section, '0' means absent one. The number 'n' could be much
> > smaller than NR_MEM_SECTIONS on most of systems.
> > 
> > |1|1|1|1|0|0|0|0|1|1|0|0|...|1|0||1|0|...|1||0|1|...|0|
> > -------------------------------------------------------
> >  0 1 2 3         4 5         i   i+1     n-1   n
> > 
> > If fail to populate the page tables to map one section's memmap, its
> > ->section_mem_map will be cleared finally to indicate that it's not present.
> > After use, these two arrays will be released at the end of sparse_init().
> > 
> > In 4-level paging mode, each array costs 4M which can be ignorable. While
> > in 5-level paging, they costs 256M each, 512M altogether. Kdump kernel
> > Usually only reserves very few memory, e.g 256M. So, even thouth they are
> > temporarily allocated, still not acceptable.
> > 
> > In fact, there's no need to allocate them with the size of NR_MEM_SECTIONS.
> > Since the ->section_mem_map clearing has been deferred to the last, the
> > number of present memory sections are kept the same during sparse_init()
> > until we finally clear out the memory section's ->section_mem_map if its
> > usemap or memmap is not correctly handled. Thus in the middle whenever
> > for_each_present_section_nr() loop is taken, the i-th present memory
> > section is always the same one.
> > 
> > Here only allocate usemap_map and map_map with the size of
> > 'nr_present_sections'. For the i-th present memory section, install its
> > usemap and memmap to usemap_map[i] and mam_map[i] during allocation. Then
> > in the last for_each_present_section_nr() loop which clears the failed
> > memory section's ->section_mem_map, fetch usemap and memmap from
> > usemap_map[] and map_map[] array and set them into mem_section[]
> > accordingly.
> > 
> > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > 
> > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > ---
> >  mm/sparse-vmemmap.c |  8 +++++---
> >  mm/sparse.c         | 40 ++++++++++++++++++++++++++--------------
> >  2 files changed, 31 insertions(+), 17 deletions(-)
> > 
> > diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> > index 640e68f8324b..f83723a49e47 100644
> > --- a/mm/sparse-vmemmap.c
> > +++ b/mm/sparse-vmemmap.c
> > @@ -281,6 +281,7 @@ void __init sparse_mem_maps_populate_node(struct page
> > **map_map,
> >  	unsigned long pnum;
> >  	unsigned long size = sizeof(struct page) * PAGES_PER_SECTION;
> >  	void *vmemmap_buf_start;
> > +	int i = 0;
> >  
> >  	size = ALIGN(size, PMD_SIZE);
> >  	vmemmap_buf_start = __earlyonly_bootmem_alloc(nodeid, size * map_count,
> > @@ -291,14 +292,15 @@ void __init sparse_mem_maps_populate_node(struct page
> > **map_map,
> >  		vmemmap_buf_end = vmemmap_buf_start + size * map_count;
> >  	}
> >  
> > -	for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
> > +	for (pnum = pnum_begin; pnum < pnum_end && i < map_count; pnum++) {
> >  		struct mem_section *ms;
> >  
> >  		if (!present_section_nr(pnum))
> >  			continue;
> >  
> > -		map_map[pnum] = sparse_mem_map_populate(pnum, nodeid, NULL);
> > -		if (map_map[pnum])
> > +		i++;
> > +		map_map[i-1] = sparse_mem_map_populate(pnum, nodeid, NULL);
> > +		if (map_map[i-1])
> >  			continue;
> >  		ms = __nr_to_section(pnum);
> >  		pr_err("%s: sparsemem memory map backing failed some memory will not be
> >  		available\n",
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index e9311b44e28a..aafb6d838872 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -405,6 +405,7 @@ static void __init sparse_early_usemaps_alloc_node(void
> > *data,
> >  	unsigned long pnum;
> >  	unsigned long **usemap_map = (unsigned long **)data;
> >  	int size = usemap_size();
> > +	int i = 0;
> >  
> >  	usemap = sparse_early_usemaps_alloc_pgdat_section(NODE_DATA(nodeid),
> >  							  size * usemap_count);
> > @@ -413,12 +414,13 @@ static void __init sparse_early_usemaps_alloc_node(void
> > *data,
> >  		return;
> >  	}
> >  
> > -	for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
> > +	for (pnum = pnum_begin; pnum < pnum_end && i < usemap_count; pnum++) {
> >  		if (!present_section_nr(pnum))
> >  			continue;
> > -		usemap_map[pnum] = usemap;
> > +		usemap_map[i] = usemap;
> >  		usemap += size;
> > -		check_usemap_section_nr(nodeid, usemap_map[pnum]);
> > +		check_usemap_section_nr(nodeid, usemap_map[i]);
> > +		i++;
> >  	}
> >  }
> >  
> > @@ -447,14 +449,17 @@ void __init sparse_mem_maps_populate_node(struct page
> > **map_map,
> >  	void *map;
> >  	unsigned long pnum;
> >  	unsigned long size = sizeof(struct page) * PAGES_PER_SECTION;
> > +	int i;
> >  
> >  	map = alloc_remap(nodeid, size * map_count);
> >  	if (map) {
> > -		for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
> > +		i = 0;
> > +		for (pnum = pnum_begin; pnum < pnum_end && i < map_count; pnum++) {
> >  			if (!present_section_nr(pnum))
> >  				continue;
> > -			map_map[pnum] = map;
> > +			map_map[i] = map;
> >  			map += size;
> > +			i++;
> >  		}
> >  		return;
> >  	}
> > @@ -464,23 +469,27 @@ void __init sparse_mem_maps_populate_node(struct page
> > **map_map,
> >  					      PAGE_SIZE, __pa(MAX_DMA_ADDRESS),
> >  					      BOOTMEM_ALLOC_ACCESSIBLE, nodeid);
> >  	if (map) {
> > -		for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
> > +		i = 0;
> > +		for (pnum = pnum_begin; pnum < pnum_end && i < map_count; pnum++) {
> >  			if (!present_section_nr(pnum))
> >  				continue;
> > -			map_map[pnum] = map;
> > +			map_map[i] = map;
> >  			map += size;
> > +			i++;
> >  		}
> >  		return;
> >  	}
> >  
> >  	/* fallback */
> > -	for (pnum = pnum_begin; pnum < pnum_end; pnum++) {
> > +	i = 0;
> > +	for (pnum = pnum_begin; pnum < pnum_end && i < map_count; pnum++) {
> >  		struct mem_section *ms;
> >  
> >  		if (!present_section_nr(pnum))
> >  			continue;
> > -		map_map[pnum] = sparse_mem_map_populate(pnum, nodeid, NULL);
> > -		if (map_map[pnum])
> > +		i++;
> > +		map_map[i-1] = sparse_mem_map_populate(pnum, nodeid, NULL);
> > +		if (map_map[i-1])
> >  			continue;
> 
> Below statement will look better?
> 
>                 map_map[i] = sparse_mem_map_populate(pnum, nodeid, NULL);
>                 if (map_map[i++])
>   			continue;

Thanks for reviewing.

It looks similar trick as the used in patch. If no other input about
this, I will update with your suggestion. And other places too.

Thanks
Baoquan

> 
> 
> >  		ms = __nr_to_section(pnum);
> >  		pr_err("%s: sparsemem memory map backing failed some memory will not be
> >  		available\n",
> > @@ -558,6 +567,7 @@ static void __init alloc_usemap_and_memmap(void
> > (*alloc_func)
> >  		/* new start, update count etc*/
> >  		nodeid_begin = nodeid;
> >  		pnum_begin = pnum;
> > +		data += map_count;
> >  		map_count = 1;
> >  	}
> >  	/* ok, last chunk */
> > @@ -576,6 +586,7 @@ void __init sparse_init(void)
> >  	unsigned long *usemap;
> >  	unsigned long **usemap_map;
> >  	int size;
> > +	int i = 0;
> >  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
> >  	int size2;
> >  	struct page **map_map;
> > @@ -598,7 +609,7 @@ void __init sparse_init(void)
> >  	 * powerpc need to call sparse_init_one_section right after each
> >  	 * sparse_early_mem_map_alloc, so allocate usemap_map at first.
> >  	 */
> > -	size = sizeof(unsigned long *) * NR_MEM_SECTIONS;
> > +	size = sizeof(unsigned long *) * nr_present_sections;
> >  	usemap_map = memblock_virt_alloc(size, 0);
> >  	if (!usemap_map)
> >  		panic("can not allocate usemap_map\n");
> > @@ -606,7 +617,7 @@ void __init sparse_init(void)
> >  							(void *)usemap_map);
> >  
> >  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
> > -	size2 = sizeof(struct page *) * NR_MEM_SECTIONS;
> > +	size2 = sizeof(struct page *) * nr_present_sections;
> >  	map_map = memblock_virt_alloc(size2, 0);
> >  	if (!map_map)
> >  		panic("can not allocate map_map\n");
> > @@ -617,14 +628,15 @@ void __init sparse_init(void)
> >  	for_each_present_section_nr(0, pnum) {
> >  		struct mem_section *ms;
> >  		ms = __nr_to_section(pnum);
> > -		usemap = usemap_map[pnum];
> > +		i++;
> > +		usemap = usemap_map[i-1];
> 
> Can try same as above and other places where possible
> 
> >  		if (!usemap) {
> >  			ms->section_mem_map = 0;
> >  			continue;
> >  		}
> >  
> >  #ifdef CONFIG_SPARSEMEM_ALLOC_MEM_MAP_TOGETHER
> > -		map = map_map[pnum];
> > +		map = map_map[i-1];
> >  #else
> >  		map = sparse_early_mem_map_alloc(pnum);
> >  #endif
> > --
> > 2.13.6
> > 
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