mem: unmap unneeded space

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@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

diff --git a/lib/librte_eal/common/eal_common_memory.c b/lib/librte_eal/common/eal_common_memory.c
index 5611a51..4f13b58 100644 (file)
--- a/lib/librte_eal/common/eal_common_memory.c
+++ b/lib/librte_eal/common/eal_common_memory.c
@@ -121,8 +121,32 @@ eal_get_virtual_area(void *requested_addr, size_t *size,
        RTE_LOG(DEBUG, EAL, "Virtual area found at %p (size = 0x%zx)\n",
                aligned_addr, *size);
 
-       if (unmap)
+       if (unmap) {
                munmap(mapped_addr, map_sz);
+       } else if (!no_align) {
+               void *map_end, *aligned_end;
+               size_t before_len, after_len;
+
+               /* when we reserve space with alignment, we add alignment to
+                * mapping size. On 32-bit, if 1GB alignment was requested, this
+                * would waste 1GB of address space, which is a luxury we cannot
+                * afford. so, if alignment was performed, check if any unneeded
+                * address space can be unmapped back.
+                */
+
+               map_end = RTE_PTR_ADD(mapped_addr, (size_t)map_sz);
+               aligned_end = RTE_PTR_ADD(aligned_addr, *size);
+
+               /* unmap space before aligned mmap address */
+               before_len = RTE_PTR_DIFF(aligned_addr, mapped_addr);
+               if (before_len > 0)
+                       munmap(mapped_addr, before_len);
+
+               /* unmap space after aligned end mmap address */
+               after_len = RTE_PTR_DIFF(map_end, aligned_end);
+               if (after_len > 0)
+                       munmap(aligned_end, after_len);
+       }
 
        baseaddr_offset += *size;