[dpdk-dev] [PATCH 2/3] memalloc: improve best-effort allocation

[Anatoly Burakov <anatoly.burakov@intel.com>]

Previously, when using non-exact allocation, we were requesting
N pages to be allocated, but allowed the memory subsystem to
allocate less than requested. However, we were still expecting
to see N contigous free pages in the memseg list.

This presents a problem because there is no way to try and
allocate as many pages as possible, even if there isn't
enough contiguous free entries in the list.

To address this, use the new "find biggest" fbarray API's when
allocating non-exact number of pages. This way, we will first
check how many entries in the list are actually available, and
then try to allocate up to that number.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---
 lib/librte_eal/linuxapp/eal/eal_memalloc.c | 33 ++++++++++++++++++----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/lib/librte_eal/linuxapp/eal/eal_memalloc.c b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
index b6fb183db..14c3ea838 100644
--- a/lib/librte_eal/linuxapp/eal/eal_memalloc.c
+++ b/lib/librte_eal/linuxapp/eal/eal_memalloc.c
@@ -874,10 +874,32 @@ alloc_seg_walk(const struct rte_memseg_list *msl, void *arg)
 	need = wa->n_segs;
 
 	/* try finding space in memseg list */
-	cur_idx = rte_fbarray_find_next_n_free(&cur_msl->memseg_arr, 0, need);
-	if (cur_idx < 0)
-		return 0;
-	start_idx = cur_idx;
+	if (wa->exact) {
+		/* if we require exact number of pages in a list, find them */
+		cur_idx = rte_fbarray_find_next_n_free(&cur_msl->memseg_arr, 0,
+				need);
+		if (cur_idx < 0)
+			return 0;
+		start_idx = cur_idx;
+	} else {
+		int cur_len;
+
+		/* we don't require exact number of pages, so we're going to go
+		 * for best-effort allocation. that means finding the biggest
+		 * unused block, and going with that.
+		 */
+		cur_idx = rte_fbarray_find_biggest_free(&cur_msl->memseg_arr,
+				0);
+		if (cur_idx < 0)
+			return 0;
+		start_idx = cur_idx;
+		/* adjust the size to possibly be smaller than original
+		 * request, but do not allow it to be bigger.
+		 */
+		cur_len = rte_fbarray_find_contig_free(&cur_msl->memseg_arr,
+				cur_idx);
+		need = RTE_MIN(need, (unsigned int)cur_len);
+	}
 
 	/* do not allow any page allocations during the time we're allocating,
 	 * because file creation and locking operations are not atomic,
@@ -954,7 +976,8 @@ alloc_seg_walk(const struct rte_memseg_list *msl, void *arg)
 		cur_msl->version++;
 	if (dir_fd >= 0)
 		close(dir_fd);
-	return 1;
+	/* if we didn't allocate any segments, move on to the next list */
+	return i > 0;
 }
 
 struct free_walk_param {
-- 
2.17.1