Re: [PATCH v3 3/4] mm: shmem: override mTHP shmem default with a kernel parameter

["Maíra Canal" <mcanal@igalia.com>]

On 31/10/24 10:33, David Hildenbrand wrote:
> On 31.10.24 14:24, Maíra Canal wrote:
>> Hi David,
>>
>> On 31/10/24 09:57, David Hildenbrand wrote:
>>> On 31.10.24 13:51, Maíra Canal wrote:
>>>> Hi David,
>>>>
>>>> On 31/10/24 09:37, David Hildenbrand wrote:
>>>>> On 30.10.24 13:58, Maíra Canal wrote:
>>>>>> Add the ``thp_shmem=`` kernel command line to allow specifying the
>>>>>> default policy of each supported shmem hugepage size. The kernel
>>>>>> parameter
>>>>>> accepts the following format:
>>>>>>
>>>>>> thp_shmem=<size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-
>>>>>> <size>[KMG]:<policy>
>>>>>>
>>>>>> For example,
>>>>>>
>>>>>> thp_shmem=16K-64K:always;128K,512K:inherit;256K:advise;1M-2M:never;4M-8M:within_size
>>>>>>
>>>>>> By configuring the default policy of several shmem hugepages, the 
>>>>>> user
>>>>>> 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         |  10 ++
>>>>>>     Documentation/admin-guide/mm/transhuge.rst    |  17 +++
>>>>>>     mm/shmem.c                                    | 109 +++++++++++++
>>>>>> ++++-
>>>>>>     3 files changed, 135 insertions(+), 1 deletion(-)
>>>>>>
>>>>
>>>> [...]
>>>>
>>>>>> diff --git a/mm/shmem.c b/mm/shmem.c
>>>>>> index dfcc88ec6e34..c2299fa0b345 100644
>>>>>> --- a/mm/shmem.c
>>>>>> +++ b/mm/shmem.c
>>>>>> @@ -136,6 +136,7 @@ static unsigned long huge_shmem_orders_always
>>>>>> __read_mostly;
>>>>>>     static unsigned long huge_shmem_orders_madvise __read_mostly;
>>>>>>     static unsigned long huge_shmem_orders_inherit __read_mostly;
>>>>>>     static unsigned long huge_shmem_orders_within_size __read_mostly;
>>>>>> +static bool shmem_orders_configured __initdata;
>>>>>>     #endif
>>>>>>     #ifdef CONFIG_TMPFS
>>>>>> @@ -5027,7 +5028,8 @@ void __init shmem_init(void)
>>>>>>          * Default to setting PMD-sized THP to inherit the global
>>>>>> setting and
>>>>>>          * disable all other multi-size THPs.
>>>>>>          */
>>>>>> -    huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
>>>>>> +    if (!shmem_orders_configured)
>>>>>> +        huge_shmem_orders_inherit = BIT(HPAGE_PMD_ORDER);
>>>>>>     #endif
>>>>>>         return;
>>>>>> @@ -5180,6 +5182,26 @@ struct kobj_attribute
>>>>>> thpsize_shmem_enabled_attr =
>>>>>>     #if defined(CONFIG_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 (BIT(order) & ~THP_ORDERS_ALL_FILE_DEFAULT)
>>>>>> +        goto err;
>>>>>> +
>>>>>> +    return order;
>>>>>> +err:
>>>>>> +    pr_err("invalid size %s in thp_shmem boot parameter\n", 
>>>>>> size_str);
>>>>>> +    return -EINVAL;
>>>>>> +}
>>>>>
>>>>> Hm, mostly copy and paste. You could reuse existing 
>>>>> get_order_from_str()
>>>>> simply by passing in the supported orders and moving error 
>>>>> reporting to
>>>>> the caller.
>>>>>
>>>>
>>>> Can I use functions from mm/huge_memory.c here?
>>>
>>> Yes, that's the idea.
>>>
>>
>> Unfortunately, it isn't possible without adding the function to a
>> header.
> 
> Well ... sure, what's the problem with that?

David & Barry, how do you feel about adding `get_order_from_str()` to
lib/cmdline.c?

Best Regards,
- Maíra

>