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

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Hi Barry,

On 28/10/24 08:09, Barry Song wrote:
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

[...]

   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".

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






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