On Thu, Apr 19, 2018 at 05:35:25PM +0100, Anatoly Burakov wrote:
> 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.bura...@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);
I suggest you take parts of the commit log and add them as a comment into
the code just after the else if.
Also, for readability, I think it would improve things to put the
munmap(unmap_pre, pre_len) immediately after the calculation of pre_len,
then a black line and then the rest of the code for clearing the post_len
block. I found it harder to decipher trying to keep track of all the
variables simultaneously in the two blocks. Splitting them into a
pre-blocka and a post-block should help here.
/Bruce
