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Re: [PATCH v2 2/2] virtio-mem: Correct default THP size for ARM64
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v2 2/2] virtio-mem: Correct default THP size for ARM64 |
Date: |
Fri, 3 Dec 2021 19:16:12 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 |
On 03.12.21 04:35, Gavin Shan wrote:
> The default block size is same as to the THP size, which is either
> retrieved from "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
> or hardcoded to 2MB. There are flaws in both mechanisms and this
> intends to fix them up.
>
> * When "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" is
> used to getting the THP size, 32MB and 512MB are valid values
> when we have 16KB and 64KB page size on ARM64.
Ah, right, there is 16KB as well :)
>
> * When the hardcoded THP size is used, 2MB, 32MB and 512MB are
> valid values when we have 4KB, 16KB and 64KB page sizes on
> ARM64.
>
> Co-developed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
> hw/virtio/virtio-mem.c | 32 ++++++++++++++++++++------------
> 1 file changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
> index ac7a40f514..8f3c95300f 100644
> --- a/hw/virtio/virtio-mem.c
> +++ b/hw/virtio/virtio-mem.c
> @@ -38,14 +38,25 @@
> */
> #define VIRTIO_MEM_MIN_BLOCK_SIZE ((uint32_t)(1 * MiB))
>
> -#if defined(__x86_64__) || defined(__arm__) || defined(__aarch64__) || \
> - defined(__powerpc64__)
> -#define VIRTIO_MEM_DEFAULT_THP_SIZE ((uint32_t)(2 * MiB))
> -#else
> - /* fallback to 1 MiB (e.g., the THP size on s390x) */
> -#define VIRTIO_MEM_DEFAULT_THP_SIZE VIRTIO_MEM_MIN_BLOCK_SIZE
> +static uint32_t virtio_mem_default_thp_size(void)
> +{
> + uint32_t default_thp_size = VIRTIO_MEM_MIN_BLOCK_SIZE;
> +
> +#if defined(__x86_64__) || defined(__arm__) || defined(__powerpc64__)
> + default_thp_size = (uint32_t)(2 * MiB);
> +#elif defined(__aarch64__)
> + if (qemu_real_host_page_size == (4 * KiB)) {
you can drop the superfluous (), also in the cases below.
> + default_thp_size = (uint32_t)(2 * MiB);
The explicit cast shouldn't be required.
> + } else if (qemu_real_host_page_size == (16 * KiB)) {
> + default_thp_size = (uint32_t)(32 * MiB);
> + } else if (qemu_real_host_page_size == (64 * KiB)) {
> + default_thp_size = (uint32_t)(512 * MiB);
> + }
> #endif
>
> + return default_thp_size;
> +}
> +
> /*
> * We want to have a reasonable default block size such that
> * 1. We avoid splitting THPs when unplugging memory, which degrades
> @@ -78,11 +89,8 @@ static uint32_t virtio_mem_thp_size(void)
> if (g_file_get_contents(HPAGE_PMD_SIZE_PATH, &content, NULL, NULL) &&
> !qemu_strtou64(content, &endptr, 0, &tmp) &&
> (!endptr || *endptr == '\n')) {
> - /*
> - * Sanity-check the value, if it's too big (e.g., aarch64 with 64k
> base
> - * pages) or weird, fallback to something smaller.
> - */
> - if (!tmp || !is_power_of_2(tmp) || tmp > 16 * MiB) {
> + /* Sanity-check the value and fallback to something reasonable. */
> + if (!tmp || !is_power_of_2(tmp)) {
> warn_report("Read unsupported THP size: %" PRIx64, tmp);
> } else {
> thp_size = tmp;
> @@ -90,7 +98,7 @@ static uint32_t virtio_mem_thp_size(void)
> }
>
> if (!thp_size) {
> - thp_size = VIRTIO_MEM_DEFAULT_THP_SIZE;
> + thp_size = virtio_mem_default_thp_size();
> warn_report("Could not detect THP size, falling back to %" PRIx64
> " MiB.", thp_size / MiB);
> }
>
Apart from that,
Reviewed-by: David Hildenbrand <david@redhat.com>
Thanks!
--
Thanks,
David / dhildenb