On 02.11.23 16:43, Wei Xu wrote:
On Wed, Nov 1, 2023 at 7:58 PM Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> wrote:
On Wed, Nov 1, 2023 at 7:40 PM Wei Xu <weixugc@xxxxxxxxxx> wrote:
On Wed, Nov 1, 2023 at 4:08 PM Sourav Panda <souravpanda@xxxxxxxxxx> 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.
I expect that the new PageMetadata field in meminfo should help break
down the memory usage of a system (MemUsed, or MemTotal - MemFree),
similar to the other fields in meminfo.
However, given that PageMetadata includes per-page metadata allocated
from not only the buddy allocator, but also the memblock allocations,
and MemTotal doesn't include memory reserved by memblock allocations,
I wonder how a user can actually use this new PageMetadata to break
down the system memory usage. BTW, it is not robust to assume that
all memblock allocations are for per-page metadata.
Hi Wei,
Here are some ideas to address this problem:
- Only report the buddy allocations for per-page medata in PageMetadata, or
Making PageMetadata not to contain all per-page memory but just some
is confusing, especially right after boot it would always be 0, as all
struct pages are all coming from memblock during boot, yet we know we
have allocated tons of memory for struct pages.
- Report per-page metadata in two separate fields in meminfo, one for
buddy allocations and another for memblock allocations, or
This is also going to be confusing for the users, it is really
implementation detail which allocator was used to allocate struct
pages, and having to trackers is not going to improve things.
- Change MemTotal/MemUsed to include the memblock reserved memory as well.
I think this is the right solution for an existing bug: MemTotal
should really include memblock reserved memory.
Adding reserved memory to MemTotal is a cleaner approach IMO as well.
But it changes the semantics of MemTotal, which may have compatibility
issues.
I object.
--
Cheers,
David / dhildenb
