[PATCH v3 0/5] page allocation tag compression

[Suren Baghdasaryan <surenb@google.com>]

This patchset implements several improvements:
1. Gracefully handles module unloading while there are used allocations
allocated from that module;
2. Provides an option to store page allocation tag references in the
page flags, removing dependency on page extensions and eliminating the
memory overhead from storing page allocation references (~0.2% of total
system memory). This also improves page allocation performance when
CONFIG_MEM_ALLOC_PROFILING is enabled by eliminating page extension
lookup. Page allocation performance overhead is reduced from 41% to 5.5%.

Patch #1 introduces mas_for_each_rev() helper function.

Patch #2 copies module tags into virtually contiguous memory which
serves two purposes:
- Lets us deal with the situation when module is unloaded while there
are still live allocations from that module. Since we are using a copy
version of the tags we can safely unload the module. Space and gaps in
this contiguous memory are managed using a maple tree.
- Enables simple indexing of the tags in the later patches.

Patch #3 changes the way we allocate virtually contiguous memory for
module tags to reserve only vitrual area and populate physical pages
only as needed at module load time.

Patch #4 abstracts page allocation tag reference to simplify later
changes.

Patch #5 adds a config to store page allocation tag references inside
page flags if they fit. If the number of available page flag bits is
insufficient to address all kernel allocations, profiling falls back
to using page extensions with an appropriate warning.

Patchset applies to mm-unstable.

Changes since v2 [1]:
- removed extra configs, leaving only CONFIG_PGALLOC_TAG_USE_PAGEFLAGS
yes/no option, per Andrew Morton
- populate physical memory for module tags only as needed,
per Pasha Tatashin

[1] https://lore.kernel.org/all/20240902044128.664075-1-surenb@google.com/

Suren Baghdasaryan (5):
  maple_tree: add mas_for_each_rev() helper
  alloc_tag: load module tags into separate contiguous memory
  alloc_tag: populate memory for module tags as needed
  alloc_tag: introduce pgalloc_tag_ref to abstract page tag references
  alloc_tag: config to store page allocation tag refs in page flags

 include/asm-generic/codetag.lds.h |  19 ++
 include/linux/alloc_tag.h         |  21 +-
 include/linux/codetag.h           |  40 ++-
 include/linux/execmem.h           |  11 +
 include/linux/maple_tree.h        |  14 ++
 include/linux/mm.h                |  25 +-
 include/linux/page-flags-layout.h |   7 +
 include/linux/pgalloc_tag.h       | 278 ++++++++++++++++++---
 include/linux/vmalloc.h           |   9 +
 kernel/module/main.c              |  74 ++++--
 lib/Kconfig.debug                 |  19 ++
 lib/alloc_tag.c                   | 394 ++++++++++++++++++++++++++++--
 lib/codetag.c                     | 104 +++++++-
 mm/execmem.c                      |  16 ++
 mm/mm_init.c                      |   5 +-
 mm/vmalloc.c                      |   4 +-
 scripts/module.lds.S              |   5 +-
 17 files changed, 931 insertions(+), 114 deletions(-)


base-commit: 828d7267c42c2aab3877c08b4bb00b1e56769557
-- 
2.47.0.rc1.288.g06298d1525-goog