On Sun, 22 Nov 2015 14:13:35 -0500
Zhihong Wang <zhihong.wang at intel.com> wrote:
> The kernel fills new allocated (huge) pages with zeros.
> DPDK just has to populate page tables to trigger the allocation.
>
> Signed-off-by: Zhihong Wang <zhihong.wang at intel.com>
> ---
> lib/librte_eal/linuxapp/eal/eal_memory.c | 20 ++++++--------------
> 1 file changed, 6 insertions(+), 14 deletions(-)
>
> diff --git a/lib/librte_eal/linuxapp/eal/eal_memory.c
> b/lib/librte_eal/linuxapp/eal/eal_memory.c
> index 0de75cd..21a5146 100644
> --- a/lib/librte_eal/linuxapp/eal/eal_memory.c
> +++ b/lib/librte_eal/linuxapp/eal/eal_memory.c
> @@ -399,8 +399,10 @@ map_all_hugepages(struct hugepage_file *hugepg_tbl,
> return -1;
> }
>
> + /* map the segment, and populate page tables,
> + * the kernel fills this segment with zeros */
> virtaddr = mmap(vma_addr, hugepage_sz, PROT_READ | PROT_WRITE,
> - MAP_SHARED, fd, 0);
> + MAP_SHARED | MAP_POPULATE, fd, 0);
> if (virtaddr == MAP_FAILED) {
> RTE_LOG(ERR, EAL, "%s(): mmap failed: %s\n", __func__,
> strerror(errno));
> @@ -410,7 +412,6 @@ map_all_hugepages(struct hugepage_file *hugepg_tbl,
>
> if (orig) {
> hugepg_tbl[i].orig_va = virtaddr;
> - memset(virtaddr, 0, hugepage_sz);
> }
> else {
> hugepg_tbl[i].final_va = virtaddr;
> @@ -529,22 +530,16 @@ remap_all_hugepages(struct hugepage_file *hugepg_tbl,
> struct hugepage_info *hpi)
>
> old_addr = vma_addr;
>
> - /* map new, bigger segment */
> + /* map new, bigger segment, and populate page tables,
> + * the kernel fills this segment with zeros */
> vma_addr = mmap(vma_addr, total_size,
> - PROT_READ | PROT_WRITE, MAP_SHARED, fd,
> 0);
> + PROT_READ | PROT_WRITE, MAP_SHARED |
> MAP_POPULATE, fd, 0);
>
> if (vma_addr == MAP_FAILED || vma_addr != old_addr) {
> RTE_LOG(ERR, EAL, "%s(): mmap failed: %s\n",
> __func__, strerror(errno));
> close(fd);
> return -1;
> }
> -
> - /* touch the page. this is needed because kernel
> postpones mapping
> - * creation until the first page fault. with this, we
> pin down
> - * the page and it is marked as used and gets into
> process' pagemap.
> - */
> - for (offset = 0; offset < total_size; offset +=
> hugepage_sz)
> - *((volatile uint8_t*) RTE_PTR_ADD(vma_addr,
> offset));
> }
>
> /* set shared flock on the file. */
> @@ -592,9 +587,6 @@ remap_all_hugepages(struct hugepage_file *hugepg_tbl,
> struct hugepage_info *hpi)
> }
> }
>
> - /* zero out the whole segment */
> - memset(hugepg_tbl[page_idx].final_va, 0, total_size);
> -
> page_idx++;
> }
>
Nice, especially on slow machines or with large memory.
Acked-by: Stephen Hemminger <stephen at networkplumber.org>
