Re: [PATCH v1] virtio-mem: don't warn about THP sizes on a kernel without THP support

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 10, 2024 at 06:34:33PM +0200, David Hildenbrand wrote:
> If the config directory in sysfs does not exist at all, we are dealing
> with a system that does not support THPs. Simply use 1 MiB block size
> then, instead of warning "Could not detect THP size, falling back to
> ..." and falling back to the default THP size.
> 
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Gavin Shan <gshan@redhat.com>
> Cc: Juraj Marcin <jmarcin@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Okay, I picked it up. But I have a question

> ---
>  hw/virtio/virtio-mem.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index ef64bf1b4a..4075f3d4ce 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -88,6 +88,7 @@ static uint32_t virtio_mem_default_thp_size(void)
>  static uint32_t thp_size;
>  
>  #define HPAGE_PMD_SIZE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
> +#define HPAGE_PATH "/sys/kernel/mm/transparent_hugepage/"


If this code runs e.g. on windows, it will poke at cwd root with
unpredictable results.
It doesn't look like this is linux specific, did I miss anything?

>  static uint32_t virtio_mem_thp_size(void)
>  {
>      gchar *content = NULL;
> @@ -98,6 +99,12 @@ static uint32_t virtio_mem_thp_size(void)
>          return thp_size;
>      }
>  
> +    /* No THP -> no restrictions. */
> +    if (!g_file_test(HPAGE_PATH, G_FILE_TEST_EXISTS)) {
> +        thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
> +        return thp_size;
> +    }
> +
>      /*
>       * Try to probe the actual THP size, fallback to (sane but eventually
>       * incorrect) default sizes.
> -- 
> 2.46.0