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 7:34 PM Maíra Canal <mcanal@igalia.com> wrote:
>
> Hi Barry,
>
> On 28/10/24 08:09, Barry Song wrote:
> > On Mon, Oct 28, 2024 at 6:10 PM Maíra Canal <mcanal@igalia.com> wrote:
> >>
> >> Hi Barry,
> >>
> >> On 27/10/24 18:54, Barry Song wrote:
> >>> 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"?
> >>
> >> 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
>
> [...]
>
> >>>>    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 :-)
>
> Let me rephrase it.
>
> I completely agree that we should avoid code duplication. I'm asking
> where is the best place to add the headers of the shared functions.
> "linux/shmem_fs.h" doesn't look appropriate to me, so I believe the
> remaining options would be "linux/huge_mm.h" or "internal.h".

Both locations seem quite odd. I have a feeling that these boot command
elements are purely internal, yet internal.h contains something that is
actually 'external' to mm. The shared code isn't 'external' enough to belong
in internal.h.

I didn't realize that shmem has placed these controls in its own file;
I thought they
were also located in mm/huge_memory.c. Given the current situation, I would
prefer to keep the code as it is and tolerate the code duplication.

Unless we are going to place controls for shmem and other thp controls in
one place, I feel your code is better than having a shared function either in
internal.h or linux/huge_mm.h.

>
> I would like to know your opinion about those two options.
>
> Best Regards,
> - Maíra
>
> >
> >>
> >> Best Regards,
> >> - Maíra
> >>
> >>>
> >>>> +__setup("thp_shmem=", setup_thp_shmem);
> >>>> +
> >>>>    #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> >>>>
> >>>>    #else /* !CONFIG_SHMEM */
> >>>> --
> >>>> 2.46.2
> >>>>
> >>>

Thanks
barry