Re: [PATCH 2/3] mm: shmem: control THP support through the kernel command line

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/10/28 01:36, Maíra Canal wrote:
> Add a new kernel command line to control the hugepage allocation policy
> for the internal shmem mount, ``transparent_hugepage_shmem``. The
> parameter is similar to ``transparent_hugepage`` and has the following
> format:
> 
> transparent_hugepage_shmem=<policy>
> 
> where ``<policy>`` is one of the seven valid policies available for
> shmem.
> 
> By configuring the default hugepage allocation policy for the internal
> shmem mount, applications that use shmem, such as the DRM GEM objects,
> 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         |  7 ++++
>   Documentation/admin-guide/mm/transhuge.rst    |  6 +++
>   mm/shmem.c                                    | 38 ++++++++++++++++++-
>   3 files changed, 49 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1666576acc0e..acabb04d0dd4 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6926,6 +6926,13 @@
>   			See Documentation/admin-guide/mm/transhuge.rst
>   			for more details.
>   
> +	transparent_hugepage_shmem= [KNL]
> +			Format: [always|within_size|advise|never|deny|force]
> +			Can be used to control the hugepage allocation policy for
> +			the internal shmem mount.
> +			See Documentation/admin-guide/mm/transhuge.rst
> +			for more details.
> +
>   	trusted.source=	[KEYS]
>   			Format: <string>
>   			This parameter identifies the trust source as a backend
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index 745055c3dc09..9b5b02c4d1ab 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -326,6 +326,12 @@ PMD_ORDER THP policy will be overridden. If the policy for PMD_ORDER
>   is not defined within a valid ``thp_anon``, its policy will default to
>   ``never``.
>   
> +Similarly to ``transparent_hugepage``, you can control the hugepage
> +allocation policy for the internal shmem mount by using the kernel parameter
> +``transparent_hugepage_shmem=<policy>``, where ``<policy>`` is one of the
> +seven valid policies for shmem (``always``, ``within_size``, ``advise``,
> +``never``, ``deny``, and ``force``).
> +
>   Hugepages in tmpfs/shmem
>   ========================
>   
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 44282a296c33..24cdeafd8260 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -582,7 +582,6 @@ static bool shmem_huge_global_enabled(struct inode *inode, pgoff_t index,
>   	}
>   }
>   
> -#if defined(CONFIG_SYSFS)
>   static int shmem_parse_huge(const char *str)
>   {
>   	if (!strcmp(str, "never"))
> @@ -599,7 +598,6 @@ static int shmem_parse_huge(const char *str)
>   		return SHMEM_HUGE_FORCE;
>   	return -EINVAL;
>   }
> -#endif
>   
>   #if defined(CONFIG_SYSFS) || defined(CONFIG_TMPFS)
>   static const char *shmem_format_huge(int huge)
> @@ -5174,6 +5172,42 @@ struct kobj_attribute thpsize_shmem_enabled_attr =
>   	__ATTR(shmem_enabled, 0644, thpsize_shmem_enabled_show, thpsize_shmem_enabled_store);
>   #endif /* CONFIG_TRANSPARENT_HUGEPAGE && CONFIG_SYSFS */
>   
> +#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
> +
> +static int __init setup_transparent_hugepage_shmem(char *str)
> +{
> +	int huge, ret = 0;
> +
> +	if (!str)
> +		goto out;
> +
> +	huge = shmem_parse_huge(str);
> +	if (huge == -EINVAL)
> +		goto out;
> +
> +	if (!has_transparent_hugepage() &&
> +			huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* Do not override huge allocation policy with non-PMD sized mTHP */
> +	if (huge == SHMEM_HUGE_FORCE &&
> +	    huge_shmem_orders_inherit != BIT(HPAGE_PMD_ORDER)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	shmem_huge = huge;

The code is similar to shmem_enabled_store(). Could you factor out the 
common parts into a helper function and reuse them?

> +	return 1;
> +out:
> +	pr_warn("transparent_hugepage_shmem= cannot parse, ignored\n");
> +	return ret;
> +}
> +__setup("transparent_hugepage_shmem=", setup_transparent_hugepage_shmem);
> +
> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> +
>   #else /* !CONFIG_SHMEM */
>   
>   /*