[dpdk-dev] [PATCH 2/2] eal/malloc: fix heap index to correctly insert memseg

[Gowrishankar]

From: Gowrishankar Muthukrishnan <gowrishankar.m at linux.vnet.ibm.com>

When there are multiple memsegs created and adding new memseg would
cause bigger heap size, its index in free_head list should be based
on new size of heap. Currently, only the size of elem is accounted
as in malloc_elem_free_list_insert. As heap total size gets bigger,
list of those memsegs should be at the right index, so that
malloc_heap_alloc would find suitable element for the requested
memory size by applications.

Fixes: b0489e7bca ("malloc: fix linear complexity")
Cc: stable at dpdk.org

Signed-off-by: Gowrishankar Muthukrishnan <gowrishankar.m at linux.vnet.ibm.com>

---
Eg. Below heap is in one numa socket, for the size of 1G (i.e 64*16MB).
All corresponding malloc_elem are always added in heap index 8,
as their size is always 16MB (and due to which, index is also 8 always).

        free_head = {{lh_first = 0x0}, {lh_first = 0x0}, {lh_first = 0x0}, {
          lh_first = 0x0}, {lh_first = 0x0}, {lh_first = 0x0}, {lh_first = 0x0}, {
          lh_first = 0x0}, {lh_first = 0x7efd3f000000}, {lh_first = 0x0}, {lh_first = 0x0}, {
          lh_first = 0x0}, {lh_first = 0x0}},
        alloc_count = 6, total_size = 1073733632},

Ideally, this list of memsegs should ideally be at slot 12, as they grow heap for 1G.
---
 lib/librte_eal/common/malloc_heap.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/librte_eal/common/malloc_heap.c b/lib/librte_eal/common/malloc_heap.c
index 1cacf7f..f686e5e 100644
--- a/lib/librte_eal/common/malloc_heap.c
+++ b/lib/librte_eal/common/malloc_heap.c
@@ -105,10 +105,32 @@
 			ms->len - MALLOC_ELEM_OVERHEAD);
 	end_elem = RTE_PTR_ALIGN_FLOOR(end_elem, RTE_CACHE_LINE_SIZE);
 	const size_t elem_size = (uintptr_t)end_elem - (uintptr_t)start_elem;
+	size_t cur_idx, new_idx, heap_size;
 
 	malloc_elem_init(start_elem, heap, ms, elem_size);
 	malloc_elem_mkend(end_elem, start_elem);
+
+	/* Compare heap index based on its current size as well as
+	 * its new size with memseg added. If new size needs new index
+	 * move its free_head to the new slot.
+	 */
+	cur_idx = malloc_elem_free_list_index(heap->total_size);
+	heap_size = heap->total_size + elem_size;
+	new_idx = malloc_elem_free_list_index(heap_size);
+	if (cur_idx != new_idx) {
+		heap->free_head[new_idx] = heap->free_head[cur_idx];
+		memset(&heap->free_head[cur_idx],
+			0, sizeof(heap->free_head[cur_idx]));
+	}
+
+	/* malloc_elem_free_list_insert calculates index based on
+	 * elem->size, hence we set elem->size as new heap size,
+	 * while inserting this elem. After that, we reset elem->size
+	 * to its original value. A minor hack though!.
+	 */
+	start_elem->size = heap_size;
 	malloc_elem_free_list_insert(start_elem);
+	start_elem->size = elem_size;
 
 	heap->total_size += elem_size;
 }
-- 
1.9.1