diff --git a/Include/internal/pycore_pymem.h b/Include/internal/pycore_pymem.h index e669a30b072d18..f3f2ae0a140828 100644 --- a/Include/internal/pycore_pymem.h +++ b/Include/internal/pycore_pymem.h @@ -88,7 +88,7 @@ extern wchar_t *_PyMem_DefaultRawWcsdup(const wchar_t *str); extern int _PyMem_DebugEnabled(void); // Enqueue a pointer to be freed possibly after some delay. -extern void _PyMem_FreeDelayed(void *ptr); +extern void _PyMem_FreeDelayed(void *ptr, size_t size); // Periodically process delayed free requests. extern void _PyMem_ProcessDelayed(PyThreadState *tstate); diff --git a/Include/internal/pycore_qsbr.h b/Include/internal/pycore_qsbr.h index b835c3abaf5d0b..1f9b3fcf777493 100644 --- a/Include/internal/pycore_qsbr.h +++ b/Include/internal/pycore_qsbr.h @@ -48,8 +48,21 @@ struct _qsbr_thread_state { // Thread state (or NULL) PyThreadState *tstate; - // Used to defer advancing write sequence a fixed number of times - int deferrals; + // Number of held items added by this thread since the last write sequence + // advance + int deferred_count; + + // Estimate for the amount of memory that is held by this thread since + // the last write sequence advance + size_t deferred_memory; + + // Amount of memory in mimalloc pages deferred from collection. When + // deferred, they are prevented from being used for a different size class + // and in a different thread. + size_t deferred_page_memory; + + // True if the deferred memory frees should be processed. + bool should_process; // Is this thread state allocated? bool allocated; @@ -109,11 +122,17 @@ _Py_qbsr_goal_reached(struct _qsbr_thread_state *qsbr, uint64_t goal) extern uint64_t _Py_qsbr_advance(struct _qsbr_shared *shared); -// Batches requests to advance the write sequence. This advances the write -// sequence every N calls, which reduces overhead but increases time to -// reclamation. Returns the new goal. +// Return the next value for the write sequence (current plus the increment). extern uint64_t -_Py_qsbr_deferred_advance(struct _qsbr_thread_state *qsbr); +_Py_qsbr_shared_next(struct _qsbr_shared *shared); + +// Return true if deferred memory frees held by QSBR should be processed to +// determine if they can be safely freed. +static inline bool +_Py_qsbr_should_process(struct _qsbr_thread_state *qsbr) +{ + return qsbr->should_process; +} // Have the read sequences advanced to the given goal? If this returns true, // it safe to reclaim any memory tagged with the goal (or earlier goal). diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-06-03-21-06-22.gh-issue-133136.Usnvri.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-03-21-06-22.gh-issue-133136.Usnvri.rst new file mode 100644 index 00000000000000..a9501c13c95b3a --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-06-03-21-06-22.gh-issue-133136.Usnvri.rst @@ -0,0 +1,2 @@ +Limit excess memory usage in the :term:`free threading` build when a +large dictionary or list is resized and accessed by multiple threads. diff --git a/Objects/codeobject.c b/Objects/codeobject.c index 3f53d4cfeb20ac..91772bc9d19098 100644 --- a/Objects/codeobject.c +++ b/Objects/codeobject.c @@ -3369,7 +3369,7 @@ create_tlbc_lock_held(PyCodeObject *co, Py_ssize_t idx) } memcpy(new_tlbc->entries, tlbc->entries, tlbc->size * sizeof(void *)); _Py_atomic_store_ptr_release(&co->co_tlbc, new_tlbc); - _PyMem_FreeDelayed(tlbc); + _PyMem_FreeDelayed(tlbc, tlbc->size * sizeof(void *)); tlbc = new_tlbc; } char *bc = PyMem_Calloc(1, _PyCode_NBYTES(co)); diff --git a/Objects/dictobject.c b/Objects/dictobject.c index 72901377cbb3da..6b7b150f0e2f2c 100644 --- a/Objects/dictobject.c +++ b/Objects/dictobject.c @@ -813,7 +813,7 @@ free_keys_object(PyDictKeysObject *keys, bool use_qsbr) { #ifdef Py_GIL_DISABLED if (use_qsbr) { - _PyMem_FreeDelayed(keys); + _PyMem_FreeDelayed(keys, _PyDict_KeysSize(keys)); return; } #endif @@ -858,7 +858,7 @@ free_values(PyDictValues *values, bool use_qsbr) assert(values->embedded == 0); #ifdef Py_GIL_DISABLED if (use_qsbr) { - _PyMem_FreeDelayed(values); + _PyMem_FreeDelayed(values, values_size_from_count(values->capacity)); return; } #endif diff --git a/Objects/listobject.c b/Objects/listobject.c index c5895645a2dd12..23d3472b6d4153 100644 --- a/Objects/listobject.c +++ b/Objects/listobject.c @@ -61,7 +61,8 @@ free_list_items(PyObject** items, bool use_qsbr) #ifdef Py_GIL_DISABLED _PyListArray *array = _Py_CONTAINER_OF(items, _PyListArray, ob_item); if (use_qsbr) { - _PyMem_FreeDelayed(array); + size_t size = sizeof(_PyListArray) + array->allocated * sizeof(PyObject *); + _PyMem_FreeDelayed(array, size); } else { PyMem_Free(array); diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c index d4b8327cb73b37..deb7fd957e57dd 100644 --- a/Objects/obmalloc.c +++ b/Objects/obmalloc.c @@ -124,6 +124,33 @@ _PyMem_mi_page_is_safe_to_free(mi_page_t *page) } +#ifdef Py_GIL_DISABLED + +// If we are deferring collection of more than this amount of memory for +// mimalloc pages, advance the write sequence. Advancing allows these +// pages to be re-used in a different thread or for a different size class. +#define QSBR_PAGE_MEM_LIMIT 4096*20 + +// Return true if the global write sequence should be advanced for a mimalloc +// page that is deferred from collection. +static bool +should_advance_qsbr_for_page(struct _qsbr_thread_state *qsbr, mi_page_t *page) +{ + size_t bsize = mi_page_block_size(page); + size_t page_size = page->capacity*bsize; + if (page_size > QSBR_PAGE_MEM_LIMIT) { + qsbr->deferred_page_memory = 0; + return true; + } + qsbr->deferred_page_memory += page_size; + if (qsbr->deferred_page_memory > QSBR_PAGE_MEM_LIMIT) { + qsbr->deferred_page_memory = 0; + return true; + } + return false; +} +#endif + static bool _PyMem_mi_page_maybe_free(mi_page_t *page, mi_page_queue_t *pq, bool force) { @@ -139,7 +166,14 @@ _PyMem_mi_page_maybe_free(mi_page_t *page, mi_page_queue_t *pq, bool force) _PyMem_mi_page_clear_qsbr(page); page->retire_expire = 0; - page->qsbr_goal = _Py_qsbr_deferred_advance(tstate->qsbr); + + if (should_advance_qsbr_for_page(tstate->qsbr, page)) { + page->qsbr_goal = _Py_qsbr_advance(tstate->qsbr->shared); + } + else { + page->qsbr_goal = _Py_qsbr_shared_next(tstate->qsbr->shared); + } + llist_insert_tail(&tstate->mimalloc.page_list, &page->qsbr_node); return false; } @@ -1141,8 +1175,44 @@ free_work_item(uintptr_t ptr, delayed_dealloc_cb cb, void *state) } } + +#ifdef Py_GIL_DISABLED + +// For deferred advance on free: the number of deferred items before advancing +// the write sequence. This is based on WORK_ITEMS_PER_CHUNK. We ideally +// want to process a chunk before it overflows. +#define QSBR_DEFERRED_LIMIT 127 + +// If the deferred memory exceeds 1 MiB, advance the write sequence. This +// helps limit memory usage due to QSBR delaying frees too long. +#define QSBR_FREE_MEM_LIMIT 1024*1024 + +// Return true if the global write sequence should be advanced for a deferred +// memory free. +static bool +should_advance_qsbr_for_free(struct _qsbr_thread_state *qsbr, size_t size) +{ + if (size > QSBR_FREE_MEM_LIMIT) { + qsbr->deferred_count = 0; + qsbr->deferred_memory = 0; + qsbr->should_process = true; + return true; + } + qsbr->deferred_count++; + qsbr->deferred_memory += size; + if (qsbr->deferred_count > QSBR_DEFERRED_LIMIT || + qsbr->deferred_memory > QSBR_FREE_MEM_LIMIT) { + qsbr->deferred_count = 0; + qsbr->deferred_memory = 0; + qsbr->should_process = true; + return true; + } + return false; +} +#endif + static void -free_delayed(uintptr_t ptr) +free_delayed(uintptr_t ptr, size_t size) { #ifndef Py_GIL_DISABLED free_work_item(ptr, NULL, NULL); @@ -1200,23 +1270,32 @@ free_delayed(uintptr_t ptr) } assert(buf != NULL && buf->wr_idx < WORK_ITEMS_PER_CHUNK); - uint64_t seq = _Py_qsbr_deferred_advance(tstate->qsbr); + uint64_t seq; + if (should_advance_qsbr_for_free(tstate->qsbr, size)) { + seq = _Py_qsbr_advance(tstate->qsbr->shared); + } + else { + seq = _Py_qsbr_shared_next(tstate->qsbr->shared); + } buf->array[buf->wr_idx].ptr = ptr; buf->array[buf->wr_idx].qsbr_goal = seq; buf->wr_idx++; if (buf->wr_idx == WORK_ITEMS_PER_CHUNK) { + // Normally the processing of delayed items is done from the eval + // breaker. Processing here is a safety measure to ensure too much + // work does not accumulate. _PyMem_ProcessDelayed((PyThreadState *)tstate); } #endif } void -_PyMem_FreeDelayed(void *ptr) +_PyMem_FreeDelayed(void *ptr, size_t size) { assert(!((uintptr_t)ptr & 0x01)); if (ptr != NULL) { - free_delayed((uintptr_t)ptr); + free_delayed((uintptr_t)ptr, size); } } @@ -1226,7 +1305,10 @@ _PyObject_XDecRefDelayed(PyObject *ptr) { assert(!((uintptr_t)ptr & 0x01)); if (ptr != NULL) { - free_delayed(((uintptr_t)ptr)|0x01); + // We use 0 as the size since we don't have an easy way to know the + // actual size. If we are freeing many objects, the write sequence + // will be advanced due to QSBR_DEFERRED_LIMIT. + free_delayed(((uintptr_t)ptr)|0x01, 0); } } #endif @@ -1317,6 +1399,8 @@ _PyMem_ProcessDelayed(PyThreadState *tstate) PyInterpreterState *interp = tstate->interp; _PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate; + tstate_impl->qsbr->should_process = false; + // Process thread-local work process_queue(&tstate_impl->mem_free_queue, tstate_impl, true, NULL, NULL); diff --git a/Python/ceval_gil.c b/Python/ceval_gil.c index 57d8f68b000b60..aa68371ac8febf 100644 --- a/Python/ceval_gil.c +++ b/Python/ceval_gil.c @@ -1387,6 +1387,10 @@ _Py_HandlePending(PyThreadState *tstate) _Py_unset_eval_breaker_bit(tstate, _PY_EVAL_EXPLICIT_MERGE_BIT); _Py_brc_merge_refcounts(tstate); } + /* Process deferred memory frees held by QSBR */ + if (_Py_qsbr_should_process(((_PyThreadStateImpl *)tstate)->qsbr)) { + _PyMem_ProcessDelayed(tstate); + } #endif /* GC scheduled to run */ diff --git a/Python/qsbr.c b/Python/qsbr.c index afa03776c26b6f..c992c285cb13e4 100644 --- a/Python/qsbr.c +++ b/Python/qsbr.c @@ -41,10 +41,6 @@ // Starting size of the array of qsbr thread states #define MIN_ARRAY_SIZE 8 -// For _Py_qsbr_deferred_advance(): the number of deferrals before advancing -// the write sequence. -#define QSBR_DEFERRED_LIMIT 10 - // Allocate a QSBR thread state from the freelist static struct _qsbr_thread_state * qsbr_allocate(struct _qsbr_shared *shared) @@ -117,13 +113,9 @@ _Py_qsbr_advance(struct _qsbr_shared *shared) } uint64_t -_Py_qsbr_deferred_advance(struct _qsbr_thread_state *qsbr) +_Py_qsbr_shared_next(struct _qsbr_shared *shared) { - if (++qsbr->deferrals < QSBR_DEFERRED_LIMIT) { - return _Py_qsbr_shared_current(qsbr->shared) + QSBR_INCR; - } - qsbr->deferrals = 0; - return _Py_qsbr_advance(qsbr->shared); + return _Py_qsbr_shared_current(shared) + QSBR_INCR; } static uint64_t pFad - Phonifier reborn

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