Re: [PATCH v1 1/1] mm: report per-page metadata information

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On Wed, Sep 13, 2023 at 10:30:00AM -0700, Sourav Panda wrote:
> Adds a new per-node PageMetadata field to
> /sys/devices/system/node/nodeN/meminfo
> and a global PageMetadata field to /proc/meminfo. This information can
> be used by users to see how much memory is being used by per-page
> metadata, which can vary depending on build configuration, machine
> architecture, and system use.
> 
> Per-page metadata is the amount of memory that Linux needs in order to
> manage memory at the page granularity. The majority of such memory is
> used by "struct page" and "page_ext" data structures.
> 
> This memory depends on build configurations, machine architectures, and
> the way system is used:
> 
> Build configuration may include extra fields into "struct page",
> and enable / disable "page_ext"
> Machine architecture defines base page sizes. For example 4K x86,
> 8K SPARC, 64K ARM64 (optionally), etc. The per-page metadata
> overhead is smaller on machines with larger page sizes.
> System use can change per-page overhead by using vmemmap
> optimizations with hugetlb pages, and emulated pmem devdax pages.
> Also, boot parameters can determine whether page_ext is needed
> to be allocated. This memory can be part of MemTotal or be outside
> MemTotal depending on whether the memory was hot-plugged, booted with,
> or hugetlb memory was returned back to the system.
> 
> Suggested-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> Signed-off-by: Sourav Panda <souravpanda@xxxxxxxxxx>
> ---
>  Documentation/filesystems/proc.rst |  3 +++
>  drivers/base/node.c                |  2 ++
>  fs/proc/meminfo.c                  |  7 +++++++
>  include/linux/mmzone.h             |  3 +++
>  include/linux/vmstat.h             |  4 ++++
>  mm/hugetlb.c                       |  8 +++++++-
>  mm/hugetlb_vmemmap.c               |  9 ++++++++-
>  mm/mm_init.c                       |  3 +++
>  mm/page_alloc.c                    |  1 +
>  mm/page_ext.c                      | 17 +++++++++++++----
>  mm/sparse-vmemmap.c                |  3 +++
>  mm/sparse.c                        |  7 ++++++-
>  mm/vmstat.c                        | 21 +++++++++++++++++++++
>  13 files changed, 81 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 2b59cff8be17..c121f2ef9432 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -987,6 +987,7 @@ Example output. You may not have all of these fields.
>      AnonPages:       4654780 kB
>      Mapped:           266244 kB
>      Shmem:              9976 kB
> +    PageMetadata:     513419 kB
>      KReclaimable:     517708 kB
>      Slab:             660044 kB
>      SReclaimable:     517708 kB
> @@ -1089,6 +1090,8 @@ Mapped
>                files which have been mmapped, such as libraries
>  Shmem
>                Total memory used by shared memory (shmem) and tmpfs
> +PageMetadata
> +              Memory used for per-page metadata
>  KReclaimable
>                Kernel allocations that the kernel will attempt to reclaim
>                under memory pressure. Includes SReclaimable (below), and other
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 493d533f8375..da728542265f 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -428,6 +428,7 @@ static ssize_t node_read_meminfo(struct device *dev,
>  			     "Node %d Mapped:         %8lu kB\n"
>  			     "Node %d AnonPages:      %8lu kB\n"
>  			     "Node %d Shmem:          %8lu kB\n"
> +			     "Node %d PageMetadata:   %8lu kB\n"
>  			     "Node %d KernelStack:    %8lu kB\n"
>  #ifdef CONFIG_SHADOW_CALL_STACK
>  			     "Node %d ShadowCallStack:%8lu kB\n"
> @@ -458,6 +459,7 @@ static ssize_t node_read_meminfo(struct device *dev,
>  			     nid, K(node_page_state(pgdat, NR_FILE_MAPPED)),
>  			     nid, K(node_page_state(pgdat, NR_ANON_MAPPED)),
>  			     nid, K(i.sharedram),
> +			     nid, K(node_page_state(pgdat, NR_PAGE_METADATA)),
>  			     nid, node_page_state(pgdat, NR_KERNEL_STACK_KB),
>  #ifdef CONFIG_SHADOW_CALL_STACK
>  			     nid, node_page_state(pgdat, NR_KERNEL_SCS_KB),
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 45af9a989d40..f141bb2a550d 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -39,7 +39,9 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  	long available;
>  	unsigned long pages[NR_LRU_LISTS];
>  	unsigned long sreclaimable, sunreclaim;
> +	unsigned long nr_page_metadata;
>  	int lru;
> +	int nid;
>  
>  	si_meminfo(&i);
>  	si_swapinfo(&i);
> @@ -57,6 +59,10 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  	sreclaimable = global_node_page_state_pages(NR_SLAB_RECLAIMABLE_B);
>  	sunreclaim = global_node_page_state_pages(NR_SLAB_UNRECLAIMABLE_B);
>  
> +	nr_page_metadata = 0;
> +	for_each_online_node(nid)
> +		nr_page_metadata += node_page_state(NODE_DATA(nid), NR_PAGE_METADATA);
> +
>  	show_val_kb(m, "MemTotal:       ", i.totalram);
>  	show_val_kb(m, "MemFree:        ", i.freeram);
>  	show_val_kb(m, "MemAvailable:   ", available);
> @@ -104,6 +110,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  	show_val_kb(m, "Mapped:         ",
>  		    global_node_page_state(NR_FILE_MAPPED));
>  	show_val_kb(m, "Shmem:          ", i.sharedram);
> +	show_val_kb(m, "PageMetadata:   ", nr_page_metadata);
>  	show_val_kb(m, "KReclaimable:   ", sreclaimable +
>  		    global_node_page_state(NR_KERNEL_MISC_RECLAIMABLE));
>  	show_val_kb(m, "Slab:           ", sreclaimable + sunreclaim);
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 4106fbc5b4b3..dda1ad522324 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -207,6 +207,9 @@ enum node_stat_item {
>  	PGPROMOTE_SUCCESS,	/* promote successfully */
>  	PGPROMOTE_CANDIDATE,	/* candidate pages to promote */
>  #endif
> +	NR_PAGE_METADATA,	/* Page metadata size (struct page and page_ext)
> +				 * in pages
> +				 */
>  	NR_VM_NODE_STAT_ITEMS
>  };
>  
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index fed855bae6d8..b5c292560f37 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -656,4 +656,8 @@ static inline void lruvec_stat_sub_folio(struct folio *folio,
>  {
>  	lruvec_stat_mod_folio(folio, idx, -folio_nr_pages(folio));
>  }
> +
> +void __init mod_node_early_perpage_metadata(int nid, long delta);
> +void __init writeout_early_perpage_metadata(void);
> +
>  #endif /* _LINUX_VMSTAT_H */
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ba6d39b71cb1..ca36751be50e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1758,6 +1758,10 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
>  		destroy_compound_gigantic_folio(folio, huge_page_order(h));
>  		free_gigantic_folio(folio, huge_page_order(h));
>  	} else {
> +#ifndef CONFIG_SPARSEMEM_VMEMMAP
> +		__mod_node_page_state(NODE_DATA(page_to_nid(&folio->page)),
> +				      NR_PAGE_METADATA, -huge_page_order(h));

I don't think memory map will change here with classic SPARSEMEM

> +#endif
>  		__free_pages(&folio->page, huge_page_order(h));
>  	}
>  }
> @@ -2143,7 +2147,9 @@ static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
>  		__count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
>  		return NULL;
>  	}
> -
> +#ifndef CONFIG_SPARSEMEM_VMEMMAP
> +	__mod_node_page_state(NODE_DATA(nid), NR_PAGE_METADATA, huge_page_order(h));
> +#endif
>  	__count_vm_event(HTLB_BUDDY_PGALLOC);
>  	return page_folio(page);
>  }
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 4b9734777f69..7f920bfa8e79 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -214,6 +214,8 @@ static inline void free_vmemmap_page(struct page *page)
>  		free_bootmem_page(page);
>  	else
>  		__free_page(page);
> +	__mod_node_page_state(NODE_DATA(page_to_nid(page)),
> +			      NR_PAGE_METADATA, -1);
>  }
>  
>  /* Free a list of the vmemmap pages */
> @@ -336,6 +338,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
>  			  (void *)walk.reuse_addr);
>  		list_add(&walk.reuse_page->lru, &vmemmap_pages);
>  	}
> +	__mod_node_page_state(NODE_DATA(nid), NR_PAGE_METADATA, 1);
>  
>  	/*
>  	 * In order to make remapping routine most efficient for the huge pages,
> @@ -387,8 +390,12 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
>  
>  	while (nr_pages--) {
>  		page = alloc_pages_node(nid, gfp_mask, 0);
> -		if (!page)
> +		if (!page) {
>  			goto out;
> +		} else {
> +			__mod_node_page_state(NODE_DATA(page_to_nid(page)),
> +					      NR_PAGE_METADATA, 1);

We can update this once for nr_pages outside the loop, cannot we?

> +		}
>  		list_add_tail(&page->lru, list);
>  	}
>  
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 50f2f34745af..e02dce7e2e9a 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -26,6 +26,7 @@
>  #include <linux/pgtable.h>
>  #include <linux/swap.h>
>  #include <linux/cma.h>
> +#include <linux/vmstat.h>
>  #include "internal.h"
>  #include "slab.h"
>  #include "shuffle.h"
> @@ -1656,6 +1657,8 @@ static void __init alloc_node_mem_map(struct pglist_data *pgdat)
>  			panic("Failed to allocate %ld bytes for node %d memory map\n",
>  			      size, pgdat->node_id);
>  		pgdat->node_mem_map = map + offset;
> +		mod_node_early_perpage_metadata(pgdat->node_id,
> +						PAGE_ALIGN(size) >> PAGE_SHIFT);
>  	}
>  	pr_debug("%s: node %d, pgdat %08lx, node_mem_map %08lx\n",
>  				__func__, pgdat->node_id, (unsigned long)pgdat,
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0c5be12f9336..4e295d5087f4 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5443,6 +5443,7 @@ void __init setup_per_cpu_pageset(void)
>  	for_each_online_pgdat(pgdat)
>  		pgdat->per_cpu_nodestats =
>  			alloc_percpu(struct per_cpu_nodestat);
> +	writeout_early_perpage_metadata();

Why it's called here?
You can copy early stats to actual node stats as soon as the nodes and page
allocator are initialized.

>  }
>  
>  __meminit void zone_pcp_init(struct zone *zone)
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 4548fcc66d74..b5b9d3079e20 100644
> --- a/mm/page_ext.c
> +++ b/mm/page_ext.c
> @@ -201,6 +201,8 @@ static int __init alloc_node_page_ext(int nid)
>  		return -ENOMEM;
>  	NODE_DATA(nid)->node_page_ext = base;
>  	total_usage += table_size;
> +	__mod_node_page_state(NODE_DATA(nid), NR_PAGE_METADATA,
> +			      PAGE_ALIGN(table_size) >> PAGE_SHIFT);
>  	return 0;
>  }
>  
> @@ -255,12 +257,15 @@ static void *__meminit alloc_page_ext(size_t size, int nid)
>  	void *addr = NULL;
>  
>  	addr = alloc_pages_exact_nid(nid, size, flags);
> -	if (addr) {
> +	if (addr)
>  		kmemleak_alloc(addr, size, 1, flags);
> -		return addr;
> -	}
> +	else
> +		addr = vzalloc_node(size, nid);
>  
> -	addr = vzalloc_node(size, nid);
> +	if (addr) {
> +		__mod_node_page_state(NODE_DATA(nid), NR_PAGE_METADATA,
> +				      PAGE_ALIGN(size) >> PAGE_SHIFT);
> +	}
>  
>  	return addr;
>  }
> @@ -314,6 +319,10 @@ static void free_page_ext(void *addr)
>  		BUG_ON(PageReserved(page));
>  		kmemleak_free(addr);
>  		free_pages_exact(addr, table_size);
> +
> +		__mod_node_page_state(NODE_DATA(page_to_nid(page)), NR_PAGE_METADATA,
> +				      (long)-1 * (PAGE_ALIGN(table_size) >> PAGE_SHIFT));
> +

what happens with vmalloc()ed page_ext?

>  	}
>  }
>  
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index a2cbe44c48e1..e33f302db7c6 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -469,5 +469,8 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
>  	if (r < 0)
>  		return NULL;
>  
> +	__mod_node_page_state(NODE_DATA(nid), NR_PAGE_METADATA,
> +			      PAGE_ALIGN(end - start) >> PAGE_SHIFT);
> +
>  	return pfn_to_page(pfn);
>  }
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 77d91e565045..db78233a85ef 100644
> --- a/mm/sparse.c
> +++ b/mm/sparse.c
> @@ -14,7 +14,7 @@
>  #include <linux/swap.h>
>  #include <linux/swapops.h>
>  #include <linux/bootmem_info.h>
> -
> +#include <linux/vmstat.h>
>  #include "internal.h"
>  #include <asm/dma.h>
>  
> @@ -465,6 +465,9 @@ static void __init sparse_buffer_init(unsigned long size, int nid)
>  	 */
>  	sparsemap_buf = memmap_alloc(size, section_map_size(), addr, nid, true);
>  	sparsemap_buf_end = sparsemap_buf + size;
> +#ifndef CONFIG_SPARSEMEM_VMEMMAP
> +	mod_node_early_perpage_metadata(nid, PAGE_ALIGN(size) >> PAGE_SHIFT);

All early struct pages are allocated in memmap_alloc(). It'd make sense to update
the counter there.

> +#endif
>  }
>  
>  static void __init sparse_buffer_fini(void)
> @@ -641,6 +644,8 @@ static void depopulate_section_memmap(unsigned long pfn, unsigned long nr_pages,
>  	unsigned long start = (unsigned long) pfn_to_page(pfn);
>  	unsigned long end = start + nr_pages * sizeof(struct page);
>  
> +	__mod_node_page_state(NODE_DATA(page_to_nid(pfn_to_page(pfn))), NR_PAGE_METADATA,
> +			      (long)-1 * (PAGE_ALIGN(end - start) >> PAGE_SHIFT));
>  	vmemmap_free(start, end, altmap);
>  }
>  static void free_map_bootmem(struct page *memmap)
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 00e81e99c6ee..731eb5264b49 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1245,6 +1245,7 @@ const char * const vmstat_text[] = {
>  	"pgpromote_success",
>  	"pgpromote_candidate",
>  #endif
> +	"nr_page_metadata",
>  
>  	/* enum writeback_stat_item counters */
>  	"nr_dirty_threshold",
> @@ -2274,4 +2275,24 @@ static int __init extfrag_debug_init(void)
>  }
>  
>  module_init(extfrag_debug_init);
> +
> +// Page metadata size (struct page and page_ext) in pages
> +unsigned long early_perpage_metadata[MAX_NUMNODES] __initdata;

static?

> +
> +void __init mod_node_early_perpage_metadata(int nid, long delta)
> +{
> +	early_perpage_metadata[nid] += delta;
> +}
> +
> +void __init writeout_early_perpage_metadata(void)
> +{
> +	int nid;
> +	struct pglist_data *pgdat;
> +
> +	for_each_online_pgdat(pgdat) {
> +		nid = pgdat->node_id;
> +		__mod_node_page_state(NODE_DATA(nid), NR_PAGE_METADATA,
> +				      early_perpage_metadata[nid]);
> +	}
> +}
>  #endif
> -- 
> 2.42.0.283.g2d96d420d3-goog
> 

-- 
Sincerely yours,
Mike.



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