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

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Message-ID: <cfcfaed5-8612-46f4-b3dd-67e1d81d049f@redhat.com>
Date: Thu, 31 Oct 2024 13:57:40 +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 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.

-- 
Cheers,

David / dhildenb