Changelog:
v7:
- Addressed comments from David Rientjes
- For exporting PageMetadata to /proc/meminfo,
utilize global_node_page_state_pages for item
NR_PAGE_METADATA. This is instead of iterating
over nodes and accumulating the output of
node_page_state.
v6:
- Interface changes
- Added per-node nr_page_metadata and
nr_page_metadata_boot fields that are exported
in /sys/devices/system/node/nodeN/vmstat
- nr_page_metadata exclusively tracks buddy
allocations while nr_page_metadata_boot
exclusively tracks memblock allocations.
- Modified PageMetadata in /proc/meminfo to only
include buddy allocations so that it is
comparable against MemTotal in /proc/meminfo
- Removed the PageMetadata field added in
/sys/devices/system/node/nodeN/meminfo
- Addressed bugs reported by the kernel test bot.
- All occurences of __mod_node_page_state have
been replaced by mod_node_page_state.
- Addressed comments from Muchun Song.
- Removed page meta data accouting from
mm/hugetlb.c. When CONFIG_SPARSEMEM_VMEMMAP
is disabled struct pages should not be returned
to buddy.
- Modified the cover letter with the results and analysis
- From when memory_hotplug.memmap_on_memory is
alternated between 0 and 1.
- To account for the new interface changes.
v5:
- Addressed comments from Muchun Song.
- Fixed errors introduced in v4 when
CONFIG_SPARSEMEM_VMEMMAP is disabled by testing
against FLATMEM and SPARSEMEM memory models.
- Handled the condition wherein the allocation of
walk.reuse_page fails, by moving NR_PAGE_METADATA
update into the clause if( walk.reuse_page ).
- Removed the usage of DIV_ROUND_UP from
alloc_vmemmap_page_list since "end - start" is
always a multiple of PAGE_SIZE.
- Modified alloc_vmemmap_page_list to update
NR_PAGE_METADATA once instead of every loop.
v4:
- Addressed comment from Matthew Wilcox.
- Used __node_stat_sub_folio and __node_stat_add_folio
instead of __mod_node_page_state in mm/hugetlb.c.
- Used page_pgdat wherever possible in the entire patch.
- Used DIV_ROUND_UP() wherever possible in the entire
patch.
v3:
- Addressed one comment from Matthew Wilcox.
- In free_page_ext, page_pgdat() is now extracted
prior to freeing the memory.
v2:
- Fixed the three bugs reported by kernel test robot.
- Enhanced the commit message as recommended by David Hildenbrand.
- Addressed comments from Matthew Wilcox:
- Simplified alloc_vmemmap_page_list() and
free_page_ext() as recommended.
- Used the appropriate comment style in mm/vmstat.c.
- Replaced writeout_early_perpage_metadata() with
store_early_perpage_metadata() to reduce ambiguity
with what swap does.
- Addressed comments from Mike Rapoport:
- Simplified the loop in alloc_vmemmap_page_list().
- Could NOT address a comment to move
store_early_perpage_metadata() near where nodes
and page allocator are initialized.
- Included the vmalloc()ed page_ext in accounting
within free_page_ext().
- Made early_perpage_metadata[MAX_NUMNODES] static.
Previous approaches and discussions
-----------------------------------
V6:
https://lore.kernel.org/all/20231205223118.3575485-1-souravpanda@xxxxxxxxxx
v5:
https://lore.kernel.org/all/20231101230816.1459373-1-souravpanda@xxxxxxxxxx
v4:
https://lore.kernel.org/all/20231031223846.827173-1-souravpanda@xxxxxxxxxx
v3:
https://lore.kernel.org/all/20231031174459.459480-1-souravpanda@xxxxxxxxxx
v2:
https://lore.kernel.org/all/20231018005548.3505662-1-souravpanda@xxxxxxxxxx
v1:
https://lore.kernel.org/r/20230913173000.4016218-2-souravpanda@xxxxxxxxxx
Hi!
This patch adds two new per-node fields, namely nr_page_metadata and
nr_page_metadata_boot to /sys/devices/system/node/nodeN/vmstat 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.
Background
----------
Kernel overhead observability is missing some of the largest
allocations during runtime, including vmemmap (struct pages) and
page_ext. This patch aims to address this problem by exporting a
new metric PageMetadata.
On the contrary, the kernel does provide observibility for boot memory
allocations. For example, the metric reserved_pages depicts the pages
allocated by the bootmem allocator. This can be simply calculated as
present_pages - managed_pages, which are both exported in /proc/zoneinfo.
The metric reserved_pages is primarily composed of struct pages and
page_ext.
What about the struct pages (allocated by bootmem allocator) that are
free'd during hugetlbfs allocations and then allocated by buddy-allocator
once hugtlbfs pages are free'd?
/proc/meminfo MemTotal changes: MemTotal does not include memblock
allocations but includes buddy allocations. However, during runtime
memblock allocations can be shifted into buddy allocations, and therefore
become part of MemTotal.
Once the struct pages get allocated by buddy allocator, we lose track of
these struct page allocations overhead accounting. Therefore, we must
export new metrics. nr_page_metadata and nr_page_metadata_boot
exclusively track the struct page and page ext allocations made by the
buddy allocator and memblock allocator, respectively for each node.
PageMetadata in /proc/meminfo would report the struct page and page ext
allocations made by the buddy allocator.
Results and analysis
--------------------
Memory model: Sparsemem-vmemmap
$ echo 1 > /proc/sys/vm/hugetlb_optimize_vmemmap
$ cat /proc/meminfo | grep MemTotal
MemTotal: 32919124 kB
$ cat /proc/meminfo | grep Meta
PageMetadata: 65536 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
AFTER HUGTLBFS RESERVATION
$ echo 512 > /proc/sys/vm/nr_hugepages
$ cat /proc/meminfo | grep MemTotal
MemTotal: 32935508 kB
$ cat /proc/meminfo | grep Meta
PageMetadata: 67584 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 8448
nr_page_metadata_boot 63488
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 8448
nr_page_metadata_booy 63488
AFTER FREEING HUGTLBFS RESERVATION
$ echo 0 > /proc/sys/vm/nr_hugepages
$ cat /proc/meminfo | grep MemTotal
MemTotal: 32935508 kB
$ cat /proc/meminfo | grep Meta
PageMetadata: 81920 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 10240
nr_page_metadata_boot 63488
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 10240
nr_page_metadata_boot 63488
------------------------
Memory Hotplug with memory_hotplug.memmap_on_memory=1
BEFORE HOTADD
$ cat /proc/meminfo | grep MemTotal
MemTotal: 32919124 kB
$ cat /proc/meminfo | grep PageMeta
PageMetadata: 65536 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
AFTER HOTADDING 1GB
$ cat /proc/meminfo | grep MemTotal
MemTotal: 33951316 kB
$ cat /proc/meminfo | grep PageMeta
PageMetadata: 83968 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 12800
nr_page_metadata_boot 65536
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
--------------------------
Memory Hotplug with memory_hotplug.memmap_on_memory=0
BEFORE HOTADD
$ cat /proc/meminfo | grep MemTotal
MemTotal: 32919124 kB
$ cat /proc/meminfo | grep PageMeta
PageMetadata: 65536 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
AFTER HOTADDING 1GB
$ cat /proc/meminfo | grep MemTotal
MemTotal: 33967700 kB
$ cat /proc/meminfo | grep PageMeta
PageMetadata: 83968 kB
$ cat /sys/devices/system/node/node0/vmstat | grep "nr_page_metadata"
nr_page_metadata 12800
nr_page_metadata_boot 65536
$ cat /sys/devices/system/node/node1/vmstat | grep "nr_page_metadata"
nr_page_metadata 8192
nr_page_metadata_boot 65536
Sourav Panda (1):
mm: report per-page metadata information
Documentation/filesystems/proc.rst | 3 +++
fs/proc/meminfo.c | 4 ++++
include/linux/mmzone.h | 4 ++++
include/linux/vmstat.h | 4 ++++
mm/hugetlb_vmemmap.c | 19 ++++++++++++++----
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, 96 insertions(+), 15 deletions(-)
--
2.43.0.429.g432eaa2c6b-goog
