Re: [Qemu-devel] [PATCH 05/15] postcopy: enhance ram_discard_range for hugepages

[Juan Quintela]

"Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> Unfortunately madvise DONTNEED doesn't work on hugepagetlb
> so use fallocate(FALLOC_FL_PUNCH_HOLE)
> qemu_fd_getpagesize only sets the page based off a file
> if the file is from hugetlbfs.
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  migration/ram.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index fe32836..7afabcd 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -45,6 +45,10 @@
>  #include "qemu/rcu_queue.h"
>  #include "migration/colo.h"
>  
> +#if defined(CONFIG_FALLOCATE_PUNCH_HOLE)
> +#include <linux/falloc.h>
> +#endif
> +
>  #ifdef DEBUG_MIGRATION_RAM
>  #define DPRINTF(fmt, ...) \
>      do { fprintf(stdout, "migration_ram: " fmt, ## __VA_ARGS__); } while (0)
> @@ -1866,7 +1870,7 @@ int ram_discard_range(MigrationIncomingState *mis,
>  
>      uint8_t *host_startaddr = rb->host + start;
>  
> -    if ((uintptr_t)host_startaddr & (qemu_host_page_size - 1)) {
> +    if ((uintptr_t)host_startaddr & (rb->page_size - 1)) {
>          error_report("ram_discard_range: Unaligned start address: %p",
>                       host_startaddr);
>          goto err;
> @@ -1874,15 +1878,27 @@ int ram_discard_range(MigrationIncomingState *mis,
>  
>      if ((start + length) <= rb->used_length) {
>          uint8_t *host_endaddr = host_startaddr + length;
> -        if ((uintptr_t)host_endaddr & (qemu_host_page_size - 1)) {
> +        if ((uintptr_t)host_endaddr & (rb->page_size - 1)) {
>              error_report("ram_discard_range: Unaligned end address: %p",
>                           host_endaddr);
>              goto err;
>          }
> -        errno = ENOTSUP;
> +        errno = ENOTSUP; /* If we are missing MADVISE etc */
> +
> +        if (rb->page_size == qemu_host_page_size) {
>  #if defined(CONFIG_MADVISE)
> -        ret = qemu_madvise(host_startaddr, length, QEMU_MADV_DONTNEED);
> +            ret = qemu_madvise(host_startaddr, length, QEMU_MADV_DONTNEED);
>  #endif
> +        } else {
> +            /* Huge page case  - unfortunately it can't do DONTNEED, but
> +             * it can do the equivalent by FALLOC_FL_PUNCH_HOLE in the
> +             * huge page file.
> +             */
> +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> +            ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | 
> FALLOC_FL_KEEP_SIZE,
> +                            start, length);
> +#endif
> +        }
>          if (ret) {
>              error_report("ram_discard_range: Failed to discard  range "
>                           "%s:%" PRIx64 " +%zx (%d)",

Can we move this to qemu-posix or similar?
qemu_punch_hole() or similar and just put all the magic there?

For the rest, I am ok with it.