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

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Message-ID: <5745d2ca-4d87-4d1f-b38f-734c7086f462@redhat.com>
Date: Thu, 31 Oct 2024 14:33:55 +0100
From: David Hildenbrand <david@...hat.com>
To: Maíra Canal <mcanal@...lia.com>,
 Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>,
 Hugh Dickins <hughd@...gle.com>, Barry Song <baohua@...nel.org>,
 Ryan Roberts <ryan.roberts@....com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>, Lance Yang <ioworker0@...il.com>
Cc: linux-mm@...ck.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel-dev@...lia.com
Subject: Re: [PATCH v3 3/4] mm: shmem: override mTHP shmem default with a
 kernel parameter

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@...lia.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?

-- 
Cheers,

David / dhildenb