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Message-ID: <CAAPL-u-0RekH-ptg9U2pzPJxCAR+jMTxKTZU49LR_isjNkSPWg@mail.gmail.com>
Date: Mon, 26 Feb 2024 10:12:32 -0800
From: Wei Xu <weixugc@...gle.com>
To: Sourav Panda <souravpanda@...gle.com>
Cc: corbet@....net, gregkh@...uxfoundation.org, rafael@...nel.org,
akpm@...ux-foundation.org, mike.kravetz@...cle.com, muchun.song@...ux.dev,
rppt@...nel.org, david@...hat.com, rdunlap@...radead.org,
chenlinxuan@...ontech.com, yang.yang29@....com.cn, tomas.mudrunka@...il.com,
bhelgaas@...gle.com, ivan@...udflare.com, pasha.tatashin@...een.com,
yosryahmed@...gle.com, hannes@...xchg.org, shakeelb@...gle.com,
kirill.shutemov@...ux.intel.com, wangkefeng.wang@...wei.com,
adobriyan@...il.com, vbabka@...e.cz, Liam.Howlett@...cle.com,
surenb@...gle.com, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org, linux-mm@...ck.org,
willy@...radead.org
Subject: Re: [PATCH v9 1/1] mm: report per-page metadata information
On Tue, Feb 20, 2024 at 1:46 PM Sourav Panda <souravpanda@...gle.com> wrote:
>
> Adds two new per-node fields, namely nr_memmap and nr_memmap_boot,
> to /sys/devices/system/node/nodeN/vmstat and a global Memmap 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.
/proc/vmstat also has the system-wide nr_memmap and nr_memmap_boot.
Given that nr_memmap in /proc/vmstat provides the same info (in
different units) as Memmap in /proc/meminfo, it would be better to
remove Memmap from /proc/meminfo to avoid duplication and confusion.
> 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. In contrast to
> most other memory consumption statistics, per-page metadata might not
> be included in MemTotal. For example, MemTotal does not include memblock
> allocations but includes buddy allocations. In this patch, exported
> field nr_memmap in /sys/devices/system/node/nodeN/vmstat would
> exclusively track buddy allocations while nr_memmap_boot would
> exclusively track memblock allocations. Furthermore, Memmap in
> /proc/meminfo would exclusively track buddy allocations allowing it to
> be compared against MemTotal.
>
> 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.
>
> Utility for userspace:
>
> Application Optimization: Depending on the kernel version and command
> line options, the kernel would relinquish a different number of pages
> (that contain struct pages) when a hugetlb page is reserved (e.g., 0, 6
> or 7 for a 2MB hugepage). The userspace application would want to know
> the exact savings achieved through page metadata deallocation without
> dealing with the intricacies of the kernel.
>
> Observability: Struct page overhead can only be calculated on-paper at
> boot time (e.g., 1.5% machine capacity). Beyond boot once hugepages are
> reserved or memory is hotplugged, the computation becomes complex.
> Per-page metrics will help explain part of the system memory overhead,
> which shall help guide memory optimizations and memory cgroup sizing.
>
> Debugging: Tracking the changes or absolute value in struct pages can
> help detect anomalies as they can be correlated with other metrics in
> the machine (e.g., memtotal, number of huge pages, etc).
>
> page_ext overheads: Some kernel features such as page_owner
> page_table_check that use page_ext can be optionally enabled via kernel
> parameters. Having the total per-page metadata information helps users
> precisely measure impact.
>
> Suggested-by: Pasha Tatashin <pasha.tatashin@...een.com>
> Signed-off-by: Sourav Panda <souravpanda@...gle.com>
> ---
> Documentation/filesystems/proc.rst | 3 +++
> fs/proc/meminfo.c | 4 ++++
> include/linux/mmzone.h | 4 ++++
> include/linux/vmstat.h | 4 ++++
> mm/hugetlb_vmemmap.c | 17 ++++++++++++----
> mm/mm_init.c | 3 +++
> mm/page_alloc.c | 1 +
> mm/page_ext.c | 32 +++++++++++++++++++++---------
> mm/sparse-vmemmap.c | 8 ++++++++
> mm/sparse.c | 7 ++++++-
> mm/vmstat.c | 26 +++++++++++++++++++++++-
> 11 files changed, 94 insertions(+), 15 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 104c6d047d9b..c9b4de65f162 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -993,6 +993,7 @@ Example output. You may not have all of these fields.
> AnonPages: 4654780 kB
> Mapped: 266244 kB
> Shmem: 9976 kB
> + Memmap: 513419 kB
> KReclaimable: 517708 kB
> Slab: 660044 kB
> SReclaimable: 517708 kB
> @@ -1095,6 +1096,8 @@ Mapped
> files which have been mmapped, such as libraries
> Shmem
> Total memory used by shared memory (shmem) and tmpfs
> +Memmap
> + 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/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 45af9a989d40..3d3db55cfeab 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -39,6 +39,7 @@ 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_memmap;
> int lru;
>
> si_meminfo(&i);
> @@ -57,6 +58,8 @@ 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_memmap = global_node_page_state_pages(NR_MEMMAP);
> +
> show_val_kb(m, "MemTotal: ", i.totalram);
> show_val_kb(m, "MemFree: ", i.freeram);
> show_val_kb(m, "MemAvailable: ", available);
> @@ -104,6 +107,7 @@ 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, "Memmap: ", nr_memmap);
> 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 a497f189d988..59b244092325 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -214,6 +214,10 @@ enum node_stat_item {
> PGDEMOTE_KSWAPD,
> PGDEMOTE_DIRECT,
> PGDEMOTE_KHUGEPAGED,
> + NR_MEMMAP, /* Page metadata size (struct page and page_ext)
> + * in pages
> + */
> + NR_MEMMAP_BOOT, /* NR_MEMMAP for bootmem */
> NR_VM_NODE_STAT_ITEMS
> };
>
> diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> index 343906a98d6e..c3785fdd3668 100644
> --- a/include/linux/vmstat.h
> +++ b/include/linux/vmstat.h
> @@ -632,4 +632,8 @@ static inline void lruvec_stat_sub_folio(struct folio *folio,
> {
> lruvec_stat_mod_folio(folio, idx, -folio_nr_pages(folio));
> }
> +
> +void __meminit mod_node_early_perpage_metadata(int nid, long delta);
> +void __meminit store_early_perpage_metadata(void);
> +
> #endif /* _LINUX_VMSTAT_H */
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index da177e49d956..2da8689aeb93 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -184,10 +184,13 @@ static int vmemmap_remap_range(unsigned long start, unsigned long end,
> */
> static inline void free_vmemmap_page(struct page *page)
> {
> - if (PageReserved(page))
> + if (PageReserved(page)) {
> free_bootmem_page(page);
> - else
> + mod_node_page_state(page_pgdat(page), NR_MEMMAP_BOOT, -1);
> + } else {
> __free_page(page);
> + mod_node_page_state(page_pgdat(page), NR_MEMMAP, -1);
> + }
> }
>
> /* Free a list of the vmemmap pages */
> @@ -338,6 +341,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
> copy_page(page_to_virt(walk.reuse_page),
> (void *)walk.reuse_addr);
> list_add(&walk.reuse_page->lru, vmemmap_pages);
> + mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, 1);
> }
>
> /*
> @@ -384,14 +388,19 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
> unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
> int nid = page_to_nid((struct page *)start);
> struct page *page, *next;
> + int i;
>
> - while (nr_pages--) {
> + for (i = 0; i < nr_pages; i++) {
> page = alloc_pages_node(nid, gfp_mask, 0);
> - if (!page)
> + if (!page) {
> + mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, i);
> goto out;
> + }
> list_add(&page->lru, list);
> }
>
> + mod_node_page_state(NODE_DATA(nid), NR_MEMMAP, nr_pages);
> +
> return 0;
> out:
> list_for_each_entry_safe(page, next, list, lru)
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 2c19f5515e36..b61372431b7d 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -27,6 +27,7 @@
> #include <linux/swap.h>
> #include <linux/cma.h>
> #include <linux/crash_dump.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,
> + DIV_ROUND_UP(size, PAGE_SIZE));
> pr_debug("%s: node %d, pgdat %08lx, node_mem_map %08lx\n",
> __func__, pgdat->node_id, (unsigned long)pgdat,
> (unsigned long)pgdat->node_mem_map);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 150d4f23b010..236cfdf5a8fa 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5635,6 +5635,7 @@ void __init setup_per_cpu_pageset(void)
> for_each_online_pgdat(pgdat)
> pgdat->per_cpu_nodestats =
> alloc_percpu(struct per_cpu_nodestat);
> + store_early_perpage_metadata();
> }
>
> __meminit void zone_pcp_init(struct zone *zone)
> diff --git a/mm/page_ext.c b/mm/page_ext.c
> index 4548fcc66d74..c1e324a1427e 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_MEMMAP_BOOT,
> + DIV_ROUND_UP(table_size, PAGE_SIZE));
> 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_MEMMAP,
> + DIV_ROUND_UP(size, PAGE_SIZE));
> + }
>
> return addr;
> }
> @@ -303,18 +308,27 @@ static int __meminit init_section_page_ext(unsigned long pfn, int nid)
>
> static void free_page_ext(void *addr)
> {
> + size_t table_size;
> + struct page *page;
> + struct pglist_data *pgdat;
> +
> + table_size = page_ext_size * PAGES_PER_SECTION;
> +
> if (is_vmalloc_addr(addr)) {
> + page = vmalloc_to_page(addr);
> + pgdat = page_pgdat(page);
> vfree(addr);
> } else {
> - struct page *page = virt_to_page(addr);
> - size_t table_size;
> -
> - table_size = page_ext_size * PAGES_PER_SECTION;
> -
> + page = virt_to_page(addr);
> + pgdat = page_pgdat(page);
> BUG_ON(PageReserved(page));
> kmemleak_free(addr);
> free_pages_exact(addr, table_size);
> }
> +
> + mod_node_page_state(pgdat, NR_MEMMAP,
> + -1L * (DIV_ROUND_UP(table_size, PAGE_SIZE)));
> +
> }
>
> static void __free_page_ext(unsigned long pfn)
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index a2cbe44c48e1..1dda6c53370b 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -469,5 +469,13 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
> if (r < 0)
> return NULL;
>
> + if (system_state == SYSTEM_BOOTING) {
> + mod_node_early_perpage_metadata(nid, DIV_ROUND_UP(end - start,
> + PAGE_SIZE));
> + } else {
> + mod_node_page_state(NODE_DATA(nid), NR_MEMMAP,
> + DIV_ROUND_UP(end - start, PAGE_SIZE));
> + }
> +
> return pfn_to_page(pfn);
> }
> diff --git a/mm/sparse.c b/mm/sparse.c
> index 338cf946dee8..eb2aeb4e226b 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, DIV_ROUND_UP(size, PAGE_SIZE));
> +#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(page_pgdat(pfn_to_page(pfn)), NR_MEMMAP,
> + -1L * (DIV_ROUND_UP(end - start, PAGE_SIZE)));
> vmemmap_free(start, end, altmap);
> }
> static void free_map_bootmem(struct page *memmap)
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index db79935e4a54..79466450040e 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1252,7 +1252,8 @@ const char * const vmstat_text[] = {
> "pgdemote_kswapd",
> "pgdemote_direct",
> "pgdemote_khugepaged",
> -
> + "nr_memmap",
> + "nr_memmap_boot",
> /* enum writeback_stat_item counters */
> "nr_dirty_threshold",
> "nr_dirty_background_threshold",
> @@ -2279,4 +2280,27 @@ static int __init extfrag_debug_init(void)
> }
>
> module_init(extfrag_debug_init);
> +
> #endif
> +
> +/*
> + * Page metadata size (struct page and page_ext) in pages
> + */
> +static unsigned long early_perpage_metadata[MAX_NUMNODES] __meminitdata;
> +
> +void __meminit mod_node_early_perpage_metadata(int nid, long delta)
> +{
> + early_perpage_metadata[nid] += delta;
> +}
> +
> +void __meminit store_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_MEMMAP_BOOT,
> + early_perpage_metadata[nid]);
> + }
> +}
> --
> 2.44.0.rc0.258.g7320e95886-goog
>
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