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

On Mon, 14 Oct 2024 13:36:41 -0700 Suren Baghdasaryan <surenb@google.com> wrote:

> 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.

Does this make "lib: alloc_tag_module_unload must wait for pending
kfree_rcu calls" unneeded?  If so, that patch was cc:stable
(justifyably), so what to do about that?

On Mon, Oct 14, 2024 at 4:32 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 14 Oct 2024 13:36:41 -0700 Suren Baghdasaryan <surenb@google.com> wrote:
>
> > 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.
>
> Does this make "lib: alloc_tag_module_unload must wait for pending
> kfree_rcu calls" unneeded?

With this change we can unload a module even when tags from that
module are still in use. However "lib: alloc_tag_module_unload must
wait for pending kfree_rcu calls" would still be useful because it
will allow us to release the memory occupied by module's tags and let
other modules use that memory.

>  If so, that patch was cc:stable (justifyably), so what to do about that?

Now that I posted this patchset I'll work on backporting "lib:
alloc_tag_module_unload must wait for pending kfree_rcu calls" and its
prerequisites to 6.10 and 6.11. I'll try to get backports out
tomorrow.
I don't think we need to backport this patchset to pre-6.12 kernels
since this is an improvement and not a bug fix. But if it's needed I
can backport it as well.
Thanks,
Suren.

On Mon, Oct 14, 2024 at 6:48 PM Suren Baghdasaryan <surenb@google.com> wrote:
>
> On Mon, Oct 14, 2024 at 4:32 PM Andrew Morton <akpm@linux-foundation.org> wrote:
> >
> > On Mon, 14 Oct 2024 13:36:41 -0700 Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > > 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.
> >
> > Does this make "lib: alloc_tag_module_unload must wait for pending
> > kfree_rcu calls" unneeded?
>
> With this change we can unload a module even when tags from that
> module are still in use. However "lib: alloc_tag_module_unload must
> wait for pending kfree_rcu calls" would still be useful because it
> will allow us to release the memory occupied by module's tags and let
> other modules use that memory.
>
> >  If so, that patch was cc:stable (justifyably), so what to do about that?
>
> Now that I posted this patchset I'll work on backporting "lib:
> alloc_tag_module_unload must wait for pending kfree_rcu calls" and its
> prerequisites to 6.10 and 6.11. I'll try to get backports out
> tomorrow.

I prepared 6.10 and 6.11 backports for
https://lore.kernel.org/all/20241007205236.11847-1-fw@strlen.de but
will wait for it to get merged into Linus' tree before posting them to
stable.
Thanks,
Suren.

> I don't think we need to backport this patchset to pre-6.12 kernels
> since this is an improvement and not a bug fix. But if it's needed I
> can backport it as well.
> Thanks,
> Suren.