[dpdk-dev] [PATCH] mem: unmap unneeded space

[Anatoly Burakov]

When we ask to reserve virtual areas, we usually include
alignment in the mapping size, and that memory ends up
being wasted. Wasting a gigabyte of VA space while trying to
reserve one gigabyte is pretty expensive on 32-bit, so after
we're done mapping, unmap unneeded space.

Signed-off-by: Anatoly Burakov <anatoly.burakov at intel.com>
---
 lib/librte_eal/common/eal_common_memory.c | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_memory.c b/lib/librte_eal/common/eal_common_memory.c
index 24a9ed5..8dd026a 100644
--- a/lib/librte_eal/common/eal_common_memory.c
+++ b/lib/librte_eal/common/eal_common_memory.c
@@ -75,8 +75,13 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
 
 	do {
 		map_sz = no_align ? *size : *size + page_sz;
+		if (map_sz > SIZE_MAX) {
+			RTE_LOG(ERR, EAL, "Map size too big\n");
+			rte_errno = E2BIG;
+			return NULL;
+		}
 
-		mapped_addr = mmap(requested_addr, map_sz, PROT_READ,
+		mapped_addr = mmap(requested_addr, (size_t)map_sz, PROT_READ,
 				mmap_flags, -1, 0);
 		if (mapped_addr == MAP_FAILED && allow_shrink)
 			*size -= page_sz;
@@ -113,8 +118,22 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
 		RTE_LOG(WARNING, EAL, "   This may cause issues with mapping memory into secondary processes\n");
 	}
 
-	if (unmap)
+	if (unmap) {
 		munmap(mapped_addr, map_sz);
+	} else if (!no_align) {
+		void *unmap_pre, *unmap_post, *map_end;
+		size_t pre_len, post_len;
+
+		/* unmap all of the extra space */
+		unmap_pre = mapped_addr;
+		pre_len = RTE_PTR_DIFF(aligned_addr, mapped_addr);
+		map_end = RTE_PTR_ADD(mapped_addr, (size_t)map_sz);
+		unmap_post = RTE_PTR_ADD(aligned_addr, *size);
+		post_len = RTE_PTR_DIFF(map_end, unmap_post);
+
+		munmap(unmap_pre, pre_len);
+		munmap(unmap_post, post_len);
+	}
 
 	RTE_LOG(DEBUG, EAL, "Virtual area found at %p (size = 0x%zx)\n",
 		aligned_addr, *size);
-- 
2.7.4