Re: [PATCH 3/3] mm: shmem: override mTHP shmem default with a kernel parameter

[Barry Song <21cnbao@gmail.com>]

On Mon, Oct 28, 2024 at 6:58 AM Maíra Canal <mcanal@igalia.com> wrote:
>
> Add the ``thp_shmem=`` kernel command line to allow specifying the
> default policy of each supported shmem hugepage size. The kernel parameter
> accepts the following format:
>
> thp_shmem=<size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy>
>
> For example,
>
> thp_shmem=16K-64K:always;128K,512K:inherit;256K:advise;1M-2M:never;4M-8M:within_size
>
> By configuring the default policy of several shmem huge pages, the user
> can take advantage of mTHP before it's been configured through sysfs.
>
> Signed-off-by: Maíra Canal <mcanal@igalia.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  10 ++
>  Documentation/admin-guide/mm/transhuge.rst    |  17 +++
>  mm/shmem.c                                    | 109 +++++++++++++++++-
>  3 files changed, 135 insertions(+), 1 deletion(-)
>

Hi Maíra,

> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index acabb04d0dd4..595fa096e28b 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6700,6 +6700,16 @@
>                         Force threading of all interrupt handlers except those
>                         marked explicitly IRQF_NO_THREAD.
>
> +       shmem_anon=     [KNL]
> +                       Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy>
> +                       Control the default policy of each hugepage size for the
> +                       internal shmem mount. <policy> is one of policies available
> +                       for the shmem mount ("always", "inherit", "never", "within_size",
> +                       and "advise").
> +                       It can be used multiple times for multiple shmem THP sizes.
> +                       See Documentation/admin-guide/mm/transhuge.rst for more
> +                       details.

I'm not sure this is the right name. How about "thp_shmem"?

> +
>         topology=       [S390,EARLY]
>                         Format: {off | on}
>                         Specify if the kernel should make use of the cpu
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index 9b5b02c4d1ab..47e7fc30e22d 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -332,6 +332,23 @@ allocation policy for the internal shmem mount by using the kernel parameter
>  seven valid policies for shmem (``always``, ``within_size``, ``advise``,
>  ``never``, ``deny``, and ``force``).
>
> +In the same manner as ``thp_anon`` controls each supported anonymous THP
> +size, ``thp_shmem`` controls each supported shmem THP size. ``thp_shmem``
> +has the same format as ``thp_anon``, but also supports the policy
> +``within_size``.
> +
> +``thp_shmem=`` may be specified multiple times to configure all THP sizes
> +as required. If ``thp_shmem=`` is specified at least once, any shmem THP
> +sizes not explicitly configured on the command line are implicitly set to
> +``never``.
> +
> +``transparent_hugepage_shmem`` setting only affects the global toggle. If
> +``thp_shmem`` is not specified, PMD_ORDER hugepage will default to
> +``inherit``. However, if a valid ``thp_shmem`` setting is provided by the
> +user, the PMD_ORDER hugepage policy will be overridden. If the policy for
> +PMD_ORDER is not defined within a valid ``thp_shmem``, its policy will
> +default to ``never``.
> +
>  Hugepages in tmpfs/shmem
>  ========================
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 24cdeafd8260..0a7a7d04f725 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -136,6 +136,7 @@ static unsigned long huge_shmem_orders_always __read_mostly;
>  static unsigned long huge_shmem_orders_madvise __read_mostly;
>  static unsigned long huge_shmem_orders_inherit __read_mostly;
>  static unsigned long huge_shmem_orders_within_size __read_mostly;
> +static bool shmem_orders_configured __initdata;
>  #endif
>
>  #ifdef CONFIG_TMPFS
> @@ -5013,7 +5014,8 @@ void __init shmem_init(void)
>          * Default to setting PMD-sized THP to inherit the global setting and
>          * disable all other multi-size THPs.
>          */
> -       huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
> +       if (!shmem_orders_configured)
> +               huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
>  #endif
>         return;
>
> @@ -5174,6 +5176,26 @@ struct kobj_attribute thpsize_shmem_enabled_attr =
>
>  #if defined(CONFIG_TRANSPARENT_HUGEPAGE)
>
> +static inline int get_order_from_str(const char *size_str)
> +{
> +       unsigned long size;
> +       char *endptr;
> +       int order;
> +
> +       size = memparse(size_str, &endptr);
> +
> +       if (!is_power_of_2(size))
> +               goto err;
> +       order = get_order(size);
> +       if (BIT(order) & ~THP_ORDERS_ALL_FILE_DEFAULT)
> +               goto err;
> +
> +       return order;
> +err:
> +       pr_err("invalid size %s in thp_shmem boot parameter\n", size_str);
> +       return -EINVAL;
> +}
> +
>  static int __init setup_transparent_hugepage_shmem(char *str)
>  {
>         int huge, ret = 0;
> @@ -5206,6 +5228,91 @@ static int __init setup_transparent_hugepage_shmem(char *str)
>  }
>  __setup("transparent_hugepage_shmem=", setup_transparent_hugepage_shmem);
>
> +static char str_dup[PAGE_SIZE] __initdata;
> +static int __init setup_thp_shmem(char *str)
> +{
> +       char *token, *range, *policy, *subtoken;
> +       unsigned long always, inherit, madvise, within_size;
> +       char *start_size, *end_size;
> +       int start, end, nr;
> +       char *p;
> +
> +       if (!str || strlen(str) + 1 > PAGE_SIZE)
> +               goto err;
> +       strcpy(str_dup, str);
> +
> +       always = huge_shmem_orders_always;
> +       inherit = huge_shmem_orders_inherit;
> +       madvise = huge_shmem_orders_madvise;
> +       within_size = huge_shmem_orders_within_size;
> +       p = str_dup;
> +       while ((token = strsep(&p, ";")) != NULL) {
> +               range = strsep(&token, ":");
> +               policy = token;
> +
> +               if (!policy)
> +                       goto err;
> +
> +               while ((subtoken = strsep(&range, ",")) != NULL) {
> +                       if (strchr(subtoken, '-')) {
> +                               start_size = strsep(&subtoken, "-");
> +                               end_size = subtoken;
> +
> +                               start = get_order_from_str(start_size);
> +                               end = get_order_from_str(end_size);
> +                       } else {
> +                               start = end = get_order_from_str(subtoken);
> +                       }
> +
> +                       if (start < 0 || end < 0 || start > end)
> +                               goto err;
> +
> +                       nr = end - start + 1;
> +                       if (!strcmp(policy, "always")) {
> +                               bitmap_set(&always, start, nr);
> +                               bitmap_clear(&inherit, start, nr);
> +                               bitmap_clear(&madvise, start, nr);
> +                               bitmap_clear(&within_size, start, nr);
> +                       } else if (!strcmp(policy, "advise")) {
> +                               bitmap_set(&madvise, start, nr);
> +                               bitmap_clear(&inherit, start, nr);
> +                               bitmap_clear(&always, start, nr);
> +                               bitmap_clear(&within_size, start, nr);
> +                       } else if (!strcmp(policy, "inherit")) {
> +                               bitmap_set(&inherit, start, nr);
> +                               bitmap_clear(&madvise, start, nr);
> +                               bitmap_clear(&always, start, nr);
> +                               bitmap_clear(&within_size, start, nr);
> +                       } else if (!strcmp(policy, "within_size")) {
> +                               bitmap_set(&within_size, start, nr);
> +                               bitmap_clear(&inherit, start, nr);
> +                               bitmap_clear(&madvise, start, nr);
> +                               bitmap_clear(&always, start, nr);
> +                       } else if (!strcmp(policy, "never")) {
> +                               bitmap_clear(&inherit, start, nr);
> +                               bitmap_clear(&madvise, start, nr);
> +                               bitmap_clear(&always, start, nr);
> +                               bitmap_clear(&within_size, start, nr);
> +                       } else {
> +                               pr_err("invalid policy %s in thp_shmem boot parameter\n", policy);
> +                               goto err;
> +                       }
> +               }
> +       }
> +
> +       huge_shmem_orders_always = always;
> +       huge_shmem_orders_madvise = madvise;
> +       huge_shmem_orders_inherit = inherit;
> +       huge_shmem_orders_within_size = within_size;
> +       shmem_orders_configured = true;
> +       return 1;
> +
> +err:
> +       pr_warn("thp_shmem=%s: error parsing string, ignoring setting\n", str);
> +       return 0;
> +}

Can we share source code with thp_anon since there's a lot of duplication?

> +__setup("thp_shmem=", setup_thp_shmem);
> +
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>
>  #else /* !CONFIG_SHMEM */
> --
> 2.46.2
>

Thanks
barry