Re: [PATCH v5] mm: override mTHP "enabled" defaults at kernel cmdline

[David Hildenbrand <david@redhat.com>]

On 17.08.24 06:55, Barry Song wrote:
> From: Ryan Roberts <ryan.roberts@arm.com>
> 
> 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>,<size>[KMG]:<value>;<size>-<size>[KMG]:<value>
> 
> An example:
> 
> thp_anon=16K-64K:always;128K,512K:inherit;256K:madvise;1M-2M:never
> 
> 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@arm.com>
> Co-developed-by: Barry Song <v-songbaohua@oppo.com>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Tested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Lance Yang <ioworker0@gmail.com>


Acked-by: David Hildenbrand <david@redhat.com>

Some nits:

> ---
>   -v5:
>   * collect Baolin's reviewed-by and tested-by tags, thanks!
>   * use get_order and check size is power 2, David, Baolin;
>   * use proper __initdata
> 
> .../admin-guide/kernel-parameters.txt         |   9 ++
>   Documentation/admin-guide/mm/transhuge.rst    |  38 +++++--
>   mm/huge_memory.c                              | 100 +++++++++++++++++-
>   3 files changed, 139 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f0057bac20fb..d0d141d50638 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6629,6 +6629,15 @@
>   			<deci-seconds>: poll all this frequency
>   			0: no polling (default)
>   
> +	thp_anon=	[KNL]
> +			Format: <size>,<size>[KMG]:<state>;<size>-<size>[KMG]:<state>
> +			state is one of "always", "madvise", "never" or "inherit".
> +			Can be used to control the default behavior of the

s/Can be used to control/Control/

> +			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 60522f49178b..4468851b6ecb 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -284,13 +284,37 @@ that THP is shared. Exceeding the number would block the collapse::
>   
>   A higher value may increase memory footprint for some workloads.

[...]

>   unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
>   					 unsigned long vm_flags,
> @@ -756,7 +757,10 @@ 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);
> +		anon_orders_configured = true;
> +	}
>   
>   	*hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
>   	if (unlikely(!*hugepage_kobj)) {
> @@ -941,6 +945,100 @@ static int __init setup_transparent_hugepage(char *str)
>   }
>   __setup("transparent_hugepage=", setup_transparent_hugepage);
>   
> +static inline int get_order_from_str(const char *size_str)
> +{
> +	unsigned long size;
> +	char *endptr;
> +	int order;
> +
> +	size = memparse(size_str, &endptr);
> +
> +	if (!is_power_of_2(size))
> +		goto err;
> +	order = get_order(size);
> +	if ((1 << order) & ~THP_ORDERS_ALL_ANON)

Could do

"if (BIT(order) & ~THP_ORDERS_ALL_ANON)"

> +		goto err;
> +
> +	return order;
> +err:
> +	pr_err("invalid size %s in thp_anon boot parameter\n", size_str);
> +	return -EINVAL;
> +}
> +
> +static char str_dup[PAGE_SIZE] __initdata;
> +static int __init setup_thp_anon(char *str)
> +{
> +	char *token, *range, *policy, *subtoken;
> +	unsigned long always, inherit, madvise;
> +	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_anon_orders_always;
> +	madvise = huge_anon_orders_madvise;
> +	inherit = huge_anon_orders_inherit;

Should we only pickup these values if "anon_orders_configured", 
otherwise start with 0? Likely that's implicit right now.

> +	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;

This only works as long as we don't have any "Holes", which is the case 
right now.

> +			if (!strcmp(policy, "always")) {
> +				bitmap_set(&always, start, nr);
> +				bitmap_clear(&inherit, start, nr);
> +				bitmap_clear(&madvise, start, nr);
> +			} else if (!strcmp(policy, "madvise")) {
> +				bitmap_set(&madvise, start, nr);
> +				bitmap_clear(&inherit, start, nr);
> +				bitmap_clear(&always, start, nr);
> +			} else if (!strcmp(policy, "inherit")) {
> +				bitmap_set(&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);
> +			} else {
> +				pr_err("invalid policy %s in thp_anon boot parameter\n", policy);
> +				goto err;
> +			}
> +		}
> +	}
> +
> +	huge_anon_orders_always = always;
> +	huge_anon_orders_madvise = madvise;
> +	huge_anon_orders_inherit = inherit;
> +	anon_orders_configured = true;
> +	return 1;
> +
> +err:
> +	pr_warn("thp_anon=%s: cannot parse, ignored\n", str);

"cannot parse, ignored" -> "error parsing string, ignoring setting" ?

> +	return 0;
> +}
> +__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))

-- 
Cheers,

David / dhildenb