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Message-ID: <d65176f1-df6f-4e21-b281-469ec958f26f@igalia.com>
Date: Thu, 31 Oct 2024 11:19:45 -0300
From: Maíra Canal <mcanal@...lia.com>
To: David Hildenbrand <david@...hat.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 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@...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?
David & Barry, how do you feel about adding `get_order_from_str()` to
lib/cmdline.c?
Best Regards,
- Maíra
>
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