Re: [Qemu-devel] [RFC v2 24/32] vub+postcopy: madvises

[Marc-André Lureau]

Hi

"libvhost-user: madvises for postcopy" for ex, would be nicer imho

On Thu, Aug 24, 2017 at 12:27 PM, Dr. David Alan Gilbert (git)
<address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> Clear the area and turn off THP.
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  contrib/libvhost-user/libvhost-user.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/contrib/libvhost-user/libvhost-user.c 
> b/contrib/libvhost-user/libvhost-user.c
> index 5ec54f7d60..d816851c6d 100644
> --- a/contrib/libvhost-user/libvhost-user.c
> +++ b/contrib/libvhost-user/libvhost-user.c
> @@ -450,11 +450,39 @@ vu_set_mem_table_exec(VuDev *dev, VhostUserMsg *vmsg)
>          }
>
>          if (dev->postcopy_listening) {
> +            int ret;
>              /* We should already have an open ufd need to mark each memory
>               * range as ufd.
> -             * Note: Do we need any madvises? Well it's not been accessed
> -             * yet, still probably need no THP to be safe, discard to be 
> safe?
>               */
> +
> +            /* Discard any mapping we have here; note I can't use MADV_REMOVE
> +             * or fallocate to make the hole since I don't want to lose
> +             * data that's already arrived in the shared process.
> +             * TODO: How to do hugepage
> +             */
> +            ret = madvise((void *)dev_region->mmap_addr,
> +                          dev_region->size + dev_region->mmap_offset,
> +                          MADV_DONTNEED);
> +            if (ret) {
> +                fprintf(stderr,
> +                        "%s: Failed to madvise(DONTNEED) region %d: %s\n",
> +                        __func__, i, strerror(errno));
> +            }
> +            /* Turn off transparent hugepages so we dont get lose wakeups
> +             * in neighbouring pages.
> +             * TODO: Turn this backon later.
> +             */
> +            ret = madvise((void *)dev_region->mmap_addr,
> +                          dev_region->size + dev_region->mmap_offset,
> +                          MADV_NOHUGEPAGE);
> +            if (ret) {
> +                /* Note: This can happen legally on kernels that are 
> configured
> +                 * without madvise'able hugepages
> +                 */
> +                fprintf(stderr,
> +                        "%s: Failed to madvise(NOHUGEPAGE) region %d: %s\n",
> +                        __func__, i, strerror(errno));
> +            }
>              struct uffdio_register reg_struct;
>              reg_struct.range.start = (uintptr_t)dev_region->mmap_addr;
>              reg_struct.range.len = dev_region->size + 
> dev_region->mmap_offset;
> --
> 2.13.5
>

Errors are non-fatal? patch looks ok to me, despite the TODOs :).
Reviewed-by: Marc-André Lureau <address@hidden>





-- 
Marc-André Lureau