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

[Daniel Gomez]

On Wed, Jul 17, 2024 at 08:12:55AM GMT, Ryan Roberts 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>

Minor suggestion. Should this be renamed to hp_anon= or hugepages_anon= instead?
This would align with the values under /sys/kernel/mm/transparent_hugepage/
hugepages-*kB.

> 
> 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.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> ---
>  .../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);

PMD_ORDER for 64k base PS systems would result in a 512M value, which exceeds
the xarray limit [1]. Therefore, I think we need to avoid PMD-size orders by
checking if PMD_ORDER > MAX_PAGECACHE_ORDER.

[1] https://lore.kernel.org/all/20240627003953.1262512-1-gshan@xxxxxxxxxx/

> +		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
>