Re: [PATCH v2 4/5] mm: shmem: add a kernel command line to change the default huge policy for tmpfs

[Daniel Gomez <da.gomez@samsung.com>]

On Tue Nov 12, 2024 at 8:45 AM CET, Baolin Wang wrote:
> Now the tmpfs can allow to allocate any sized large folios, and the default
> huge policy is still 'never'. Thus adding a new command line to change
> the default huge policy will be helpful to use the large folios for tmpfs,
> which is similar to the 'transparent_hugepage_shmem' cmdline for shmem.


I think it would be good to include a summary of why tmpfs is not
enabling large folios by default as the other fs. David has been
pretty good at repeating the reasons over and over and it would be very
valuable to have them included here.

>
> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  7 ++++++
>  Documentation/admin-guide/mm/transhuge.rst    |  6 +++++
>  mm/shmem.c                                    | 23 ++++++++++++++++++-
>  3 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index b48d744d99b0..007e6cfada3e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6943,6 +6943,13 @@
>  			See Documentation/admin-guide/mm/transhuge.rst
>  			for more details.
>  
> +	transparent_hugepage_tmpfs= [KNL]
> +			Format: [always|within_size|advise|never]
> +			Can be used to control the default hugepage allocation policy
> +			for the tmpfs 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 5034915f4e8e..9ae775eaacbe 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -332,6 +332,12 @@ 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``).
>  
> +Similarly to ``transparent_hugepage_shmem``, you can control the default
> +hugepage allocation policy for the tmpfs mount by using the kernel parameter
> +``transparent_hugepage_tmpfs=<policy>``, where ``<policy>`` is one of the
> +four valid policies for tmpfs (``always``, ``within_size``, ``advise``,
> +``never``). The tmpfs mount default policy is ``never``.
> +
>  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
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a3203cf8860f..021760e91cea 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -548,6 +548,7 @@ static bool shmem_confirm_swap(struct address_space *mapping,
>  /* ifdef here to avoid bloating shmem.o when not necessary */
>  
>  static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER;
> +static int tmpfs_huge __read_mostly = SHMEM_HUGE_NEVER;
>  
>  /**
>   * shmem_mapping_size_orders - Get allowable folio orders for the given file size.
> @@ -4780,7 +4781,12 @@ static int shmem_fill_super(struct super_block *sb, struct fs_context *fc)
>  	sbinfo->gid = ctx->gid;
>  	sbinfo->full_inums = ctx->full_inums;
>  	sbinfo->mode = ctx->mode;
> -	sbinfo->huge = ctx->huge;
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	if (ctx->seen & SHMEM_SEEN_HUGE)
> +		sbinfo->huge = ctx->huge;
> +	else
> +		sbinfo->huge = tmpfs_huge;
> +#endif
>  	sbinfo->mpol = ctx->mpol;
>  	ctx->mpol = NULL;
>  
> @@ -5259,6 +5265,21 @@ static int __init setup_transparent_hugepage_shmem(char *str)
>  }
>  __setup("transparent_hugepage_shmem=", setup_transparent_hugepage_shmem);
>  
> +static int __init setup_transparent_hugepage_tmpfs(char *str)
> +{
> +	int huge;
> +
> +	huge = shmem_parse_huge(str);
> +	if (huge < 0) {
> +		pr_warn("transparent_hugepage_tmpfs= cannot parse, ignored\n");
> +		return huge;
> +	}
> +
> +	tmpfs_huge = huge;
> +	return 1;
> +}
> +__setup("transparent_hugepage_tmpfs=", setup_transparent_hugepage_tmpfs);
> +
>  static char str_dup[PAGE_SIZE] __initdata;
>  static int __init setup_thp_shmem(char *str)
>  {