Function prof_recent_alloc

BeefRT/JEMalloc/src/prof_recent.c:278–403

}

void
prof_recent_alloc(tsd_t *tsd, edata_t *edata, size_t size, size_t usize) {
	cassert(config_prof);
	assert(edata != NULL);
	prof_tctx_t *tctx = edata_prof_tctx_get(edata);

	malloc_mutex_assert_not_owner(tsd_tsdn(tsd), tctx->tdata->lock);
	malloc_mutex_lock(tsd_tsdn(tsd), &prof_recent_alloc_mtx);
	prof_recent_alloc_assert_count(tsd);

	/*
	 * Reserve a new prof_recent_t node if needed.  If needed, we release
	 * the prof_recent_alloc_mtx lock and allocate.  Then, rather than
	 * immediately checking for OOM, we regain the lock and try to make use
	 * of the reserve node if needed.  There are six scenarios:
	 *
	 *          \ now | no need | need but OOMed | need and allocated
	 *     later \    |         |                |
	 *    ------------------------------------------------------------
	 *     no need    |   (1)   |      (2)       |         (3)
	 *    ------------------------------------------------------------
	 *     need       |   (4)   |      (5)       |         (6)
	 *
	 * First, "(4)" never happens, because we don't release the lock in the
	 * middle if there's no need for a new node; in such cases "(1)" always
	 * takes place, which is trivial.
	 *
	 * Out of the remaining four scenarios, "(6)" is the common case and is
	 * trivial.  "(5)" is also trivial, in which case we'll rollback the
	 * effect of prof_recent_alloc_prepare() as expected.
	 *
	 * "(2)" / "(3)" occurs when the need for a new node is gone after we
	 * regain the lock.  If the new node is successfully allocated, i.e. in
	 * the case of "(3)", we'll release it in the end; otherwise, i.e. in
	 * the case of "(2)", we do nothing - we're lucky that the OOM ends up
	 * doing no harm at all.
	 *
	 * Therefore, the only performance cost of the "release lock" ->
	 * "allocate" -> "regain lock" design is the "(3)" case, but it happens
	 * very rarely, so the cost is relatively small compared to the gain of
	 * not having to have the lock order of prof_recent_alloc_mtx above all
	 * the allocation locks.
	 */
	prof_recent_t *reserve = NULL;
	if (prof_recent_alloc_max_get(tsd) == -1 ||
	    prof_recent_alloc_count < prof_recent_alloc_max_get(tsd)) {
		assert(prof_recent_alloc_max_get(tsd) != 0);
		malloc_mutex_unlock(tsd_tsdn(tsd), &prof_recent_alloc_mtx);
		reserve = prof_recent_allocate_node(tsd_tsdn(tsd));
		malloc_mutex_lock(tsd_tsdn(tsd), &prof_recent_alloc_mtx);
		prof_recent_alloc_assert_count(tsd);
	}

	if (prof_recent_alloc_max_get(tsd) == 0) {
		assert(prof_recent_alloc_is_empty(tsd));
		goto label_rollback;
	}