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

[Ryan Roberts]

On 22/07/2024 10:13, Daniel Gomez wrote:
> 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.

"hp" doesn't feel right; that's not an abreviation we use today to my knowledge.
But I'd be happy to change it to "hugepages_anon", if that's the concensus.

> 
>>
>> 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.

This is for anon memory, which isn't installed in the page cache so its
independent of MAX_PAGECACHE_ORDER. I don't believe there is a problem here.

> 
> [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