[PATCH v2 0/6] page allocation tag compression

Suren Baghdasaryan
2024-09-02T04:41:33Z

This patchset implements several improvements:
1. Gracefully handles module unloading while there are used allocations
allocated from that module;
2. Provides an option to reduce memory overhead from storing page
allocation references by indexing allocation tags;
3. 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).
4. Improves page allocation performance when CONFIG_MEM_ALLOC_PROFILING
is enabled by eliminating page extension lookup. Page allocation
performance overhead is reduced from 14% 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.

Preallocated virtually contiguous memory size can be configured using
max_module_alloc_tags kernel parameter.

Patch #3 is a code cleanup to simplify later changes.

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

Patch #5 lets us control page allocation tag reference sizes and
introduces tag indexing.

Patch #6 adds a config to store page allocation tag references inside
page flags if they fit.

Patchset applies to mm-unstable.

Changes since v1 [1]:
- introduced mas_for_each_rev() and use it, per Liam Howlett
- use advanced maple_tree API to minimize lookups, per Liam Howlett
- fixed CONFIG_MODULES=n configuration build, per kernel test robot

[1] https://lore.kernel.org/all/20240819151512.2363698-1-surenb@google.com/

Suren Baghdasaryan (6):
maple_tree: add mas_for_each_rev() helper
alloc_tag: load module tags into separate continuous memory
alloc_tag: eliminate alloc_tag_ref_set
alloc_tag: introduce pgalloc_tag_ref to abstract page tag references
alloc_tag: make page allocation tag reference size configurable
alloc_tag: config to store page allocation tag refs in page flags

.../admin-guide/kernel-parameters.txt | 4 +
include/asm-generic/codetag.lds.h | 19 ++
include/linux/alloc_tag.h | 46 ++-
include/linux/codetag.h | 40 ++-
include/linux/maple_tree.h | 14 +
include/linux/mmzone.h | 3 +
include/linux/page-flags-layout.h | 10 +-
include/linux/pgalloc_tag.h | 287 +++++++++++++---
kernel/module/main.c | 67 ++--
lib/Kconfig.debug | 36 +-
lib/alloc_tag.c | 321 ++++++++++++++++--
lib/codetag.c | 104 +++++-
mm/mm_init.c | 1 +
mm/page_ext.c | 2 +-
scripts/module.lds.S | 5 +-
15 files changed, 826 insertions(+), 133 deletions(-)

base-commit: 18d35b7e30d5a217ff1cc976bb819e1aa2873301
--
2.46.0.469.g59c65b2a67-goog