Re: [PATCH v4 1/1] mm: report per-page metadata information

From: Muchun Song
Date: Thu Nov 02 2023 - 22:24:38 EST

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In reply to: Muchun Song: "Re: [PATCH v4 1/1] mm: report per-page metadata information"
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> On Nov 3, 2023, at 01:37, Sourav Panda <souravpanda@xxxxxxxxxx> wrote:
>
>
>
> On Wed, Nov 1, 2023 at 7:43 PM Muchun Song <muchun.song@xxxxxxxxx> wrote:
>
>
> > On Nov 2, 2023, at 06:58, Sourav Panda <souravpanda@xxxxxxxxxx> wrote:
> >
> >
> >
> > On Tue, Oct 31, 2023 at 8:38 PM Muchun Song <muchun.song@xxxxxxxxx> 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@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 | 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?
>
> Thank you again!
>
> I see both your points. I believe the solution is to remove updates to NR_PAGE_METADATA
> when CONFIG_SPARSEMEM_VMEMMAP is disabled. I shall do this in v6 if you agree.
>
> Why is it added with a PAGE_SIZE?
> - You are correct. First of all we should not even update it when CONFIG_SPARSEMEM_VMEMMAP
> is disabled. Furthermore, even if we did, we should have done it by a factor of
> huge_page_order(h) instead of folio_nr_pages(folio).

Actually, I think we should remove this counting from this path regardless of
whether CONFIG_SPARSEMEM_VMEMMAP is enabled or not. The metadata (aka page structure)
is not allocated from here, it is allocated from where the vmemmap areas are
initialized during boot time. You should count there.

> - This error was introduced in v4 as we switched from
> __mod_node_page_state(pg_dat, NR_PAGE_METADATA, huge_page_order(h)) to
> __node_stat_sub_folio(folio, NR_PAGE_METADATA).
> - huge_page_order(h) returns 9 for each 2 MB HugeTLB page allocation while
> folio_nr_pages(folio), which is called in __node_stat_sub_folio returns 512.
> - Removing updates to NR_PAGE_METADATA when CONFIG_SPARSEMEM_VMEMMAP is
> disabled shall fix this problem.
>
>
> > 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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