Re: [RFC PATCH v1 3/4] mm: Override mTHP "enabled" defaults at kernel cmdline

[Barry Song <baohua@kernel.org>]

On Fri, Jul 19, 2024 at 7:48 PM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> On 19/07/2024 01:46, Barry Song wrote:
> > On Wed, Jul 17, 2024 at 7:13 PM Ryan Roberts <ryan.roberts@arm.com> wrote:
> >>
> >> Add thp_anon= cmdline parameter to allow specifying the default
> >> enablement of each supported anon THP size. The parameter accepts the
> >> following format and can be provided multiple times to configure each
> >> size:
> >>
> >> thp_anon=<size>[KMG]:<value>
> >>
> >> See Documentation/admin-guide/mm/transhuge.rst for more details.
> >>
> >> Configuring the defaults at boot time is useful to allow early user
> >> space to take advantage of mTHP before its been configured through
> >> sysfs.
> >
> > This is exactly what I need and want to implement, as the current behavior
> > is problematic. We need to boot up the system and reach the point where
> > we can set up the sys interfaces to enable mTHP. Many processes miss the
> > opportunity to use mTHP.
> >
> > On the other hand, userspace might have been tuned to detect that mTHP
> > is enabled, such as a .so library. However, it turns out we have had
> > inconsistent settings between the two stages - before and after setting
> > mTHP enabled by sys interfaces.
>
> Good feedback - sounds like I should separate out this patch from the rest of
> the series to get it reviewed and merged faster?

+1

>
> >
> >>
> >> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> >> ---
> >>  .../admin-guide/kernel-parameters.txt         |  8 +++
> >>  Documentation/admin-guide/mm/transhuge.rst    | 26 +++++++--
> >>  mm/huge_memory.c                              | 55 ++++++++++++++++++-
> >>  3 files changed, 82 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> >> index bc55fb55cd26..48443ad12e3f 100644
> >> --- a/Documentation/admin-guide/kernel-parameters.txt
> >> +++ b/Documentation/admin-guide/kernel-parameters.txt
> >> @@ -6592,6 +6592,14 @@
> >>                         <deci-seconds>: poll all this frequency
> >>                         0: no polling (default)
> >>
> >> +       thp_anon=       [KNL]
> >> +                       Format: <size>[KMG]:always|madvise|never|inherit
> >> +                       Can be used to control the default behavior of the
> >> +                       system with respect to anonymous transparent hugepages.
> >> +                       Can be used multiple times for multiple anon THP sizes.
> >> +                       See Documentation/admin-guide/mm/transhuge.rst for more
> >> +                       details.
> >> +
> >>         threadirqs      [KNL,EARLY]
> >>                         Force threading of all interrupt handlers except those
> >>                         marked explicitly IRQF_NO_THREAD.
> >> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> >> index 1aaf8e3a0b5a..f53d43d986e2 100644
> >> --- a/Documentation/admin-guide/mm/transhuge.rst
> >> +++ b/Documentation/admin-guide/mm/transhuge.rst
> >> @@ -311,13 +311,27 @@ performance.
> >>  Note that any changes to the allowed set of sizes only applies to future
> >>  file-backed THP allocations.
> >>
> >> -Boot parameter
> >> -==============
> >> +Boot parameters
> >> +===============
> >>
> >> -You can change the sysfs boot time defaults of Transparent Hugepage
> >> -Support by passing the parameter ``transparent_hugepage=always`` or
> >> -``transparent_hugepage=madvise`` or ``transparent_hugepage=never``
> >> -to the kernel command line.
> >> +You can change the sysfs boot time default for the top-level "enabled"
> >> +control by passing the parameter ``transparent_hugepage=always`` or
> >> +``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` to the
> >> +kernel command line.
> >> +
> >> +Alternatively, each supported anonymous THP size can be controlled by
> >> +passing ``thp_anon=<size>[KMG]:<state>``, where ``<size>`` is the THP size
> >> +and ``<state>`` is one of ``always``, ``madvise``, ``never`` or
> >> +``inherit``.
> >> +
> >> +For example, the following will set 64K THP to ``always``::
> >> +
> >> +       thp_anon=64K:always
> >> +
> >> +``thp_anon=`` may be specified multiple times to configure all THP sizes as
> >> +required. If ``thp_anon=`` is specified at least once, any anon THP sizes
> >> +not explicitly configured on the command line are implicitly set to
> >> +``never``.
> >>
> >>  Hugepages in tmpfs/shmem
> >>  ========================
> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> >> index 4249c0bc9388..794d2790d90d 100644
> >> --- a/mm/huge_memory.c
> >> +++ b/mm/huge_memory.c
> >> @@ -82,6 +82,7 @@ unsigned long huge_anon_orders_madvise __read_mostly;
> >>  unsigned long huge_anon_orders_inherit __read_mostly;
> >>  unsigned long huge_file_orders_always __read_mostly;
> >>  int huge_file_exec_order __read_mostly = -1;
> >> +static bool anon_orders_configured;
> >>
> >>  unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
> >>                                          unsigned long vm_flags,
> >> @@ -763,7 +764,10 @@ static int __init hugepage_init_sysfs(struct kobject **hugepage_kobj)
> >>          * disable all other sizes. powerpc's PMD_ORDER isn't a compile-time
> >>          * constant so we have to do this here.
> >>          */
> >> -       huge_anon_orders_inherit = BIT(PMD_ORDER);
> >> +       if (!anon_orders_configured) {
> >> +               huge_anon_orders_inherit = BIT(PMD_ORDER);
> >> +               anon_orders_configured = true;
> >> +       }
> >>
> >>         /*
> >>          * For pagecache, default to enabling all orders. powerpc's PMD_ORDER
> >> @@ -955,6 +959,55 @@ static int __init setup_transparent_hugepage(char *str)
> >>  }
> >>  __setup("transparent_hugepage=", setup_transparent_hugepage);
> >>
> >> +static int __init setup_thp_anon(char *str)
> >> +{
> >> +       unsigned long size;
> >> +       char *state;
> >> +       int order;
> >> +       int ret = 0;
> >> +
> >> +       if (!str)
> >> +               goto out;
> >> +
> >> +       size = (unsigned long)memparse(str, &state);
> >> +       order = ilog2(size >> PAGE_SHIFT);
> >> +       if (*state != ':' || !is_power_of_2(size) || size <= PAGE_SIZE ||
> >> +           !(BIT(order) & THP_ORDERS_ALL_ANON))
> >> +               goto out;
> >> +
> >> +       state++;
> >> +
> >> +       if (!strcmp(state, "always")) {
> >> +               clear_bit(order, &huge_anon_orders_inherit);
> >> +               clear_bit(order, &huge_anon_orders_madvise);
> >> +               set_bit(order, &huge_anon_orders_always);
> >> +               ret = 1;
> >> +       } else if (!strcmp(state, "inherit")) {
> >> +               clear_bit(order, &huge_anon_orders_always);
> >> +               clear_bit(order, &huge_anon_orders_madvise);
> >> +               set_bit(order, &huge_anon_orders_inherit);
> >> +               ret = 1;
> >> +       } else if (!strcmp(state, "madvise")) {
> >> +               clear_bit(order, &huge_anon_orders_always);
> >> +               clear_bit(order, &huge_anon_orders_inherit);
> >> +               set_bit(order, &huge_anon_orders_madvise);
> >> +               ret = 1;
> >> +       } else if (!strcmp(state, "never")) {
> >> +               clear_bit(order, &huge_anon_orders_always);
> >> +               clear_bit(order, &huge_anon_orders_inherit);
> >> +               clear_bit(order, &huge_anon_orders_madvise);
> >> +               ret = 1;
> >> +       }
> >> +
> >> +       if (ret)
> >> +               anon_orders_configured = true;
> >> +out:
> >> +       if (!ret)
> >> +               pr_warn("thp_anon=%s: cannot parse, ignored\n", str);
> >> +       return ret;
> >> +}
> >> +__setup("thp_anon=", setup_thp_anon);
> >> +
> >>  pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma)
> >>  {
> >>         if (likely(vma->vm_flags & VM_WRITE))
> >> --
> >> 2.43.0
> >>
> >
> > Thanks
> > Barry
>
>