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Date:   Thu, 2 Nov 2023 10:43:00 +0800
From:   Muchun Song <muchun.song@...ux.dev>
To:     Sourav Panda <souravpanda@...gle.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Greg KH <gregkh@...uxfoundation.org>, rafael@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        chenlinxuan@...ontech.com, yang.yang29@....com.cn,
        tomas.mudrunka@...il.com, bhelgaas@...gle.com, ivan@...udflare.com,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>, adobriyan@...il.com,
        Vlastimil Babka <vbabka@...e.cz>, Liam.Howlett@...cle.com,
        surenb@...gle.com, LKML <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Matthew Wilcox <willy@...radead.org>, weixugc@...gle.com
Subject: Re: [PATCH v4 1/1] mm: report per-page metadata information



> On Nov 2, 2023, at 06:58, Sourav Panda <souravpanda@...gle.com> wrote:
> 
> 
> 
> On Tue, Oct 31, 2023 at 8:38 PM Muchun Song <muchun.song@...ux.dev> wrote:
> 
> 
> On 2023/11/1 06:38, 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. 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. While on the other hand,
> > per-page metadata would include both memblock and buddy allocations.
> >
> > 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@...een.com>
> > Signed-off-by: Sourav Panda <souravpanda@...gle.com>
> > ---
> >   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                       | 11 ++++++++--
> >   mm/hugetlb_vmemmap.c               |  8 ++++++--
> >   mm/mm_init.c                       |  3 +++
> >   mm/page_alloc.c                    |  1 +
> >   mm/page_ext.c                      | 32 +++++++++++++++++++++---------
> >   mm/sparse-vmemmap.c                |  3 +++
> >   mm/sparse.c                        |  7 ++++++-
> >   mm/vmstat.c                        | 24 ++++++++++++++++++++++
> >   13 files changed, 94 insertions(+), 14 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..af096a881f03 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 store_early_perpage_metadata(void);
> > +
> >   #endif /* _LINUX_VMSTAT_H */
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 1301ba7b2c9a..cd3158a9c7f3 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1790,6 +1790,9 @@ 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
> > +             __node_stat_sub_folio(folio, NR_PAGE_METADATA);
> > +#endif
> >               __free_pages(&folio->page, huge_page_order(h));
> >       }
> >   }
> > @@ -2125,6 +2128,7 @@ static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
> >       struct page *page;
> >       bool alloc_try_hard = true;
> >       bool retry = true;
> > +     struct folio *folio;
> >   
> >       /*
> >        * By default we always try hard to allocate the page with
> > @@ -2175,9 +2179,12 @@ static struct folio *alloc_buddy_hugetlb_folio(struct hstate *h,
> >               __count_vm_event(HTLB_BUDDY_PGALLOC_FAIL);
> >               return NULL;
> >       }
> > -
> > +     folio = page_folio(page);
> > +#ifndef CONFIG_SPARSEMEM_VMEMMAP
> > +     __node_stat_add_folio(folio, NR_PAGE_METADATA)
> 
> Seems you have not tested this patch with CONFIG_SPARSEMEM_VMEMMAP disabled.
> You missed ";" in the end.
> 
> Thanks for reviewing this patch. I will submit v5 by testing against FLATMEM and
> SPARSEMEM (VMEMMAP disabled) memory model on ARM32. This error was introduced
> in v4.
> 
>  
> > +#endif
> 
> I am curious why we should account HugeTLB pages as metadata.
> 
> When HugeTLB pages are reserved, memory pertaining to redundant `struct page` are
> returned to the buddy allocator for other uses. This essentially reflects the change in the

Why the `struct page` are returned to the buddy when CONFIG_SPARSEMEM_VMEMMAP
is disabled? Why it is added with a PAGE_SIZE?

> amount of `struct pages` when HugeTLB pages are reserved and free'd.
>  
> >       __count_vm_event(HTLB_BUDDY_PGALLOC);
> > -     return page_folio(page);
> > +     return folio;
> >   }
> >   
> >   /*
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index 4b9734777f69..804a93d18cab 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -214,6 +214,7 @@ static inline void free_vmemmap_page(struct page *page)
> >               free_bootmem_page(page);
> >       else
> >               __free_page(page);
> > +     __mod_node_page_state(page_pgdat(page), NR_PAGE_METADATA, -1);
> >   }
> >   
> >   /* Free a list of the vmemmap pages */
> > @@ -336,6 +337,7 @@ 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);
> 
> What if allocation of walk.reuse_page fails?
> 
> Thank you for pointing this out. I will move the NR_PAGE_METADATA update within the 
> if ( walk.reuse_page ) clause to cover the case where walk.reuse_page fails.
>  
> >   
> >       /*
> >        * In order to make remapping routine most efficient for the huge pages,
> > @@ -381,14 +383,16 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
> >                                  struct list_head *list)
> >   {
> >       gfp_t gfp_mask = GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_THISNODE;
> > -     unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
> > +     unsigned long nr_pages = DIV_ROUND_UP(end - start, PAGE_SIZE);
> 
> "end - start" is always multiple of PAGE_SIZE, why we need DIV_ROUND_UP 
> here?
> 
> Thank you. I agree with this and will revert this change in v5.
>  
> >       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)
> >                       goto out;
> > +             __mod_node_page_state(page_pgdat(page), NR_PAGE_METADATA, 1);
> >               list_add_tail(&page->lru, list);
> >       }
> 
> Count one by ine is really inefficient. Can't we count *nr_pages* at
> one time?
> 
> Thanks for suggesting this optimization. I will modify the implementation to update the
> metadata once as opposed to every iteration.
>  
> >   
> > diff --git a/mm/mm_init.c b/mm/mm_init.c
> > index 50f2f34745af..6997bf00945b 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,
> > +                                             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,
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 85741403948f..522dc0c52610 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);
> > +     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..d8d6db9c3d75 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,
> > +                           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_PAGE_METADATA,
> > +                                 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_PAGE_METADATA,
> > +                           -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..2bc67b2c2aa2 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,
> > +                           DIV_ROUND_UP(end - start, PAGE_SIZE));
> > +
> >       return pfn_to_page(pfn);
> >   }
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 77d91e565045..7f67b5486cd1 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_PAGE_METADATA,
> > +                           -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 00e81e99c6ee..070d2b3d2bcc 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 +2275,27 @@ 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] __initdata;
> > +
> > +void __init mod_node_early_perpage_metadata(int nid, long delta)
> > +{
> > +     early_perpage_metadata[nid] += delta;
> > +}
> > +
> > +void __init 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_PAGE_METADATA,
> > +                                   early_perpage_metadata[nid]);
> > +     }
> > +}


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