Add output argument to hpa_purge_begin to count dirty ranges

include/jemalloc/internal/hpdata.h

@@ -395,9 +395,11 @@ struct hpdata_purge_state_s {
  * until you're done, and then end.  Allocating out of an hpdata undergoing
  * purging is not allowed.
  *
- * Returns the number of dirty pages that will be purged.
+ * Returns the number of dirty pages that will be purged and sets nranges
+ * to number of ranges with dirty pages that will be purged.
  */
-size_t hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state);
+size_t hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state,
+    size_t *nranges);
 
 /*
  * If there are more extents to purge, sets *r_purge_addr and *r_purge_size to

src/hpa.c

@@ -465,8 +465,10 @@ hpa_try_purge(tsdn_t *tsdn, hpa_shard_t *shard) {
 
 	/* Gather all the metadata we'll need during the purge. */
 	bool dehugify = hpdata_huge_get(to_purge);
+	size_t nranges;
 	hpdata_purge_state_t purge_state;
-	size_t num_to_purge = hpdata_purge_begin(to_purge, &purge_state);
+	size_t num_to_purge = hpdata_purge_begin(to_purge, &purge_state, &nranges);
+	(void) nranges; /*not used yet */
 
 	shard->npending_purge += num_to_purge;
 

src/hpdata.c

@@ -164,7 +164,8 @@ hpdata_unreserve(hpdata_t *hpdata, void *addr, size_t sz) {
 }
 
 size_t
-hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state) {
+hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state,
+	size_t *nranges) {
 	hpdata_assert_consistent(hpdata);
 	/*
 	 * See the comment below; we might purge any inactive extent, so it's
@@ -216,6 +217,7 @@ hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state) {
 
 	fb_init(purge_state->to_purge, HUGEPAGE_PAGES);
 	size_t next_bit = 0;
+	*nranges = 0;
 	while (next_bit < HUGEPAGE_PAGES) {
 		size_t next_dirty = fb_ffs(dirty_pages, HUGEPAGE_PAGES,
 		    next_bit);
@@ -239,6 +241,7 @@ hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state) {
 
 		fb_set_range(purge_state->to_purge, HUGEPAGE_PAGES, next_dirty,
 		    last_dirty - next_dirty + 1);
+		(*nranges)++;
 		next_bit = next_active + 1;
 	}
 
@@ -249,6 +252,8 @@ hpdata_purge_begin(hpdata_t *hpdata, hpdata_purge_state_t *purge_state) {
 	    purge_state->to_purge, HUGEPAGE_PAGES, 0, HUGEPAGE_PAGES));
 	assert(ndirty == fb_scount(dirty_pages, HUGEPAGE_PAGES, 0,
 	    HUGEPAGE_PAGES));
+	assert(*nranges <= ndirty);
+	assert(ndirty == 0 || *nranges > 0);
 
 	hpdata_assert_consistent(hpdata);
 

test/unit/hpdata.c

@@ -69,8 +69,10 @@ TEST_BEGIN(test_purge_simple) {
 
 	hpdata_alloc_allowed_set(&hpdata, false);
 	hpdata_purge_state_t purge_state;
-	size_t to_purge = hpdata_purge_begin(&hpdata, &purge_state);
+	size_t nranges;
+	size_t to_purge = hpdata_purge_begin(&hpdata, &purge_state, &nranges);
 	expect_zu_eq(HUGEPAGE_PAGES / 4, to_purge, "");
+	expect_zu_eq(1, nranges, "All dirty pages in a single range");
 
 	void *purge_addr;
 	size_t purge_size;
@@ -113,8 +115,10 @@ TEST_BEGIN(test_purge_intervening_dalloc) {
 
 	hpdata_alloc_allowed_set(&hpdata, false);
 	hpdata_purge_state_t purge_state;
-	size_t to_purge = hpdata_purge_begin(&hpdata, &purge_state);
+	size_t nranges;
+	size_t to_purge = hpdata_purge_begin(&hpdata, &purge_state, &nranges);
 	expect_zu_eq(HUGEPAGE_PAGES / 2, to_purge, "");
+	expect_zu_eq(2, nranges, "First quarter and last half");
 
 	void *purge_addr;
 	size_t purge_size;
@@ -171,8 +175,10 @@ TEST_BEGIN(test_purge_over_retained) {
 	/* Purge the second quarter. */
 	hpdata_alloc_allowed_set(&hpdata, false);
 	hpdata_purge_state_t purge_state;
-	size_t to_purge_dirty = hpdata_purge_begin(&hpdata, &purge_state);
+	size_t nranges;
+	size_t to_purge_dirty = hpdata_purge_begin(&hpdata, &purge_state, &nranges);
 	expect_zu_eq(HUGEPAGE_PAGES / 4, to_purge_dirty, "");
+	expect_zu_eq(1, nranges, "Second quarter only");
 
 	bool got_result = hpdata_purge_next(&hpdata, &purge_state, &purge_addr,
 	    &purge_size);
@@ -199,8 +205,9 @@ TEST_BEGIN(test_purge_over_retained) {
 	 * re-purge it.  We expect a single purge of 3/4 of the hugepage,
 	 * purging half its pages.
 	 */
-	to_purge_dirty = hpdata_purge_begin(&hpdata, &purge_state);
+	to_purge_dirty = hpdata_purge_begin(&hpdata, &purge_state, &nranges);
 	expect_zu_eq(HUGEPAGE_PAGES / 2, to_purge_dirty, "");
+	expect_zu_eq(1, nranges, "Single range expected");
 
 	got_result = hpdata_purge_next(&hpdata, &purge_state, &purge_addr,
 	    &purge_size);

test/unit/psset.c

@@ -19,7 +19,9 @@ static void
 test_psset_fake_purge(hpdata_t *ps) {
 	hpdata_purge_state_t purge_state;
 	hpdata_alloc_allowed_set(ps, false);
-	hpdata_purge_begin(ps, &purge_state);
+	size_t nranges;
+	hpdata_purge_begin(ps, &purge_state, &nranges);
+	(void) nranges;
 	void *addr;
 	size_t size;
 	while (hpdata_purge_next(ps, &purge_state, &addr, &size)) {