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

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On Mon, Oct 28, 2024 at 6:10 PM Maíra Canal <mcanal@xxxxxxxxxx> wrote:
>
> Hi Barry,
>
> On 27/10/24 18:54, Barry Song wrote:
> > On Mon, Oct 28, 2024 at 6:58 AM Maíra Canal <mcanal@xxxxxxxxxx> 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@xxxxxxxxxx>
> >> ---
> >>   .../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"?
>
> Oops, sorry about that.
>
> >
> >> +
> >>          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?
>
> I'm not a regular mm contributor and I'm most usually around drivers, so
> I don't know exactly here I could add shared code. Should I add the
> headers to "internal.h"?

My comment isn't related to drivers or memory management. It's solely about
avoiding code duplication. For example, we could create a shared function to
handle both controls, reducing redundant code :-)

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





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