Fix mimalloc allocator for huge memory allocation (around
8,589,934,592 GiB) on s390x.
Abort allocation early in mimalloc if the number of slices doesn't
fit into uint32_t, to prevent a integer overflow (cast 64-bit
size_t to uint32_t).
This implements the delayed reuse of mimalloc pages that contain Python
objects in the free-threaded build.
Allocations of the same size class are grouped in data structures called
pages. These are different from operating system pages. For thread-safety, we
want to ensure that memory used to store PyObjects remains valid as long as
there may be concurrent lock-free readers; we want to delay using it for
other size classes, in other heaps, or returning it to the operating system.
When a mimalloc page becomes empty, instead of immediately freeing it, we tag
it with a QSBR goal and insert it into a per-thread state linked list of
pages to be freed. When mimalloc needs a fresh page, we process the queue and
free any still empty pages that are now deemed safe to be freed. Pages
waiting to be freed are still available for allocations of the same size
class and allocating from a page prevent it from being freed. There is
additional logic to handle abandoned pages when threads exit.
This adds support for visiting abandoned pages in mimalloc and improves
the performance of the page visiting code. Abandoned pages contain
memory blocks from threads that have exited. At some point, they may be
later reclaimed by other threads. We still need to visit those pages in
the free-threaded GC because they contain live objects.
This also reduces the overhead of visiting mimalloc pages:
* Special cases for full, empty, and pages containing only a single
block.
* Fix free_map to use one bit instead of one byte per block.
* Use fast integer division by a constant algorithm when computing
block offset from block size and index.
* gh-112532: Tag mimalloc heaps and pages
Mimalloc pages are data structures that contain contiguous allocations
of the same block size. Note that they are distinct from operating
system pages. Mimalloc pages are contained in segments.
When a thread exits, it abandons any segments and contained pages that
have live allocations. These segments and pages may be later reclaimed
by another thread. To support GC and certain thread-safety guarantees in
free-threaded builds, we want pages to only be reclaimed by the
corresponding heap in the claimant thread. For example, we want pages
containing GC objects to only be claimed by GC heaps.
This allows heaps and pages to be tagged with an integer tag that is
used to ensure that abandoned pages are only claimed by heaps with the
same tag. Heaps can be initialized with a tag (0-15); any page allocated
by that heap copies the corresponding tag.
* Fix conversion warning
* gh-112532: Isolate abandoned segments by interpreter
Mimalloc segments are data structures that contain memory allocations along
with metadata. Each segment is "owned" by a thread. When a thread exits,
it abandons its segments to a global pool to be later reclaimed by other
threads. This changes the pool to be per-interpreter instead of process-wide.
This will be important for when we use mimalloc to find GC objects in the
`--disable-gil` builds. We want heaps to only store Python objects from a
single interpreter. Absent this change, the abandoning and reclaiming process
could break this isolation.
* Add missing '&_mi_abandoned_default' to 'tld_empty'
* Add mimalloc v2.12
Modified src/alloc.c to remove include of alloc-override.c and not
compile new handler.
Did not include the following files:
- include/mimalloc-new-delete.h
- include/mimalloc-override.h
- src/alloc-override-osx.c
- src/alloc-override.c
- src/static.c
- src/region.c
mimalloc is thread safe and shares a single heap across all runtimes,
therefore finalization and getting global allocated blocks across all
runtimes is different.
* mimalloc: minimal changes for use in Python:
- remove debug spam for freeing large allocations
- use same bytes (0xDD) for freed allocations in CPython and mimalloc
This is important for the test_capi debug memory tests
* Don't export mimalloc symbol in libpython.
* Enable mimalloc as Python allocator option.
* Add mimalloc MIT license.
* Log mimalloc in Lib/test/pythoninfo.py.
* Document new mimalloc support.
* Use macro defs for exports as done in:
https://github.com/python/cpython/pull/31164/
Co-authored-by: Sam Gross <colesbury@gmail.com>
Co-authored-by: Christian Heimes <christian@python.org>
Co-authored-by: Victor Stinner <vstinner@python.org>
Victor Stinner
Sam Gross
Dino Viehland