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Message-ID: <f50a4630-c3bf-4af5-a17f-133ef599e705@arm.com>
Date: Fri, 9 Aug 2024 09:57:14 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Barry Song <baohua@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Jonathan Corbet <corbet@....net>, David Hildenbrand <david@...hat.com>,
Lance Yang <ioworker0@...il.com>, Baolin Wang
<baolin.wang@...ux.alibaba.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: Override mTHP "enabled" defaults at kernel cmdline
On 09/08/2024 09:31, Barry Song wrote:
> On Fri, Aug 9, 2024 at 3:58 PM Ryan Roberts <ryan.roberts@....com> wrote:
>>
>> On 08/08/2024 22:17, Barry Song wrote:
>>> On Thu, Aug 8, 2024 at 10:17 PM Ryan Roberts <ryan.roberts@....com> wrote:
>>>>
>>>> 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>[KMG]:<value>
>>>>
>>>> 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@....com>
>>>> ---
>>>>
>>>> Hi All,
>>>>
>>>> I've split this off from my RFC at [1] because Barry highlighted that he would
>>>> benefit from it immediately [2]. There are no changes vs the version in that
>>>> series.
>>>>
>>>> It applies against today's mm-unstable (275d686abcb59). (although I had to fix a
>>>> minor build bug in stackdepot.c due to MIN() not being defined in this tree).
>>>>
>>>> Thanks,
>>>> Ryan
>>>>
>>>>
>>>> .../admin-guide/kernel-parameters.txt | 8 +++
>>>> Documentation/admin-guide/mm/transhuge.rst | 26 +++++++--
>>>> mm/huge_memory.c | 55 ++++++++++++++++++-
>>>> 3 files changed, 82 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>>> index bcdee8984e1f0..5c79b58c108ec 100644
>>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>>> @@ -6631,6 +6631,14 @@
>>>> <deci-seconds>: poll all this frequency
>>>> 0: no polling (default)
>>>>
>>>> + thp_anon= [KNL]
>>>> + Format: <size>[KMG]:always|madvise|never|inherit
>>>> + Can be used to control the default behavior of the
>>>> + 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 24eec1c03ad88..f63b0717366c6 100644
>>>> --- a/Documentation/admin-guide/mm/transhuge.rst
>>>> +++ b/Documentation/admin-guide/mm/transhuge.rst
>>>> @@ -284,13 +284,27 @@ that THP is shared. Exceeding the number would block the collapse::
>>>>
>>>> A higher value may increase memory footprint for some workloads.
>>>>
>>>> -Boot parameter
>>>> -==============
>>>> +Boot parameters
>>>> +===============
>>>>
>>>> -You can change the sysfs boot time defaults of Transparent Hugepage
>>>> -Support by passing the parameter ``transparent_hugepage=always`` or
>>>> -``transparent_hugepage=madvise`` or ``transparent_hugepage=never``
>>>> -to the kernel command line.
>>>> +You can change the sysfs boot time default for the top-level "enabled"
>>>> +control by passing the parameter ``transparent_hugepage=always`` or
>>>> +``transparent_hugepage=madvise`` or ``transparent_hugepage=never`` to the
>>>> +kernel command line.
>>>> +
>>>> +Alternatively, each supported anonymous THP size can be controlled by
>>>> +passing ``thp_anon=<size>[KMG]:<state>``, where ``<size>`` is the THP size
>>>> +and ``<state>`` is one of ``always``, ``madvise``, ``never`` or
>>>> +``inherit``.
>>>> +
>>>> +For example, the following will set 64K THP to ``always``::
>>>> +
>>>> + thp_anon=64K:always
>>>> +
>>>> +``thp_anon=`` may be specified multiple times to configure all THP sizes as
>>>> +required. If ``thp_anon=`` is specified at least once, any anon THP sizes
>>>> +not explicitly configured on the command line are implicitly set to
>>>> +``never``.
>>>>
>>>> Hugepages in tmpfs/shmem
>>>> ========================
>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>> index 0c3075ee00012..c2c0da1eb94e6 100644
>>>> --- a/mm/huge_memory.c
>>>> +++ b/mm/huge_memory.c
>>>> @@ -82,6 +82,7 @@ unsigned long huge_zero_pfn __read_mostly = ~0UL;
>>>> unsigned long huge_anon_orders_always __read_mostly;
>>>> unsigned long huge_anon_orders_madvise __read_mostly;
>>>> unsigned long huge_anon_orders_inherit __read_mostly;
>>>> +static bool anon_orders_configured;
>>>>
>>>> unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
>>>> unsigned long vm_flags,
>>>> @@ -672,7 +673,10 @@ 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;
>>>> + }
>>>
>>> If a user configures 64KB and doesn't adjust anything for PMD_ORDER,
>>> then PMD_ORDER will be set to "never", correct? This seems to change
>>> the default behavior of PMD_ORDER. Could we instead achieve this by
>>> checking if PMD_ORDER has been explicitly configured?
>>
>> Yes, that's how it's implemented in this patch, and the accompanying docs also
>> state:
>>
>> If ``thp_anon=`` is specified at least once, any anon THP sizes
>> not explicitly configured on the command line are implicitly set to
>> ``never``.
>>
>> My initial approach did exactly as you suggest. But in the original series, I
>> also had a similar patch to configure file thp with "thp_file=". And for file,
>> all of the orders default to `always`. So if taking the same approach with that
>> control, the user would have to explicitly opt-out of all supported orders
>> rather than just opt-in to the orders they want. And I thought that could get
>> tricky in future if support is added for more orders. I felt that was
>> potentially very confusing so decided it was clearer to have the above rule and
>> make both controls consistent.
>>
>> What do you think?
>
> If this is the intention, once the user sets the command line, they should
> realize that the default settings have been overridden. I am perfectly fine
> with this strategy.
OK. I can see it from both sides to be honest. Let's see if anyone else has
issue with this approach.
>
> with the below cmdline:
> thp_anon=64K:always thp_anon=8K:inherit thp_anon=32K:madvise
> thp_anon=1M:inherit thp_anon=2M:always
>
> I am getting:
> / # cat /sys/kernel/mm/transparent_hugepage/hugepages-64kB/enabled
> [always] inherit madvise never
> / # cat /sys/kernel/mm/transparent_hugepage/hugepages-32kB/enabled
> always inherit [madvise] never
> / # cat /sys/kernel/mm/transparent_hugepage/hugepages-1024kB/enabled
> always [inherit] madvise never
> / # cat /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled
> [always] inherit madvise never
And you should also be seeing a warning in the boot log that thp_anon=8K:inherit
is unrecognised (since anon doesn't support order-1).
>
> Thus,
>
> Tested-by: Barry Song <baohua@...nel.org>
Thanks!
>
>>
>>
>>>
>>>>
>>>> *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
>>>> if (unlikely(!*hugepage_kobj)) {
>>>> @@ -857,6 +861,55 @@ static int __init setup_transparent_hugepage(char *str)
>>>> }
>>>> __setup("transparent_hugepage=", setup_transparent_hugepage);
>>>>
>>>> +static int __init setup_thp_anon(char *str)
>>>> +{
>>>> + unsigned long size;
>>>> + char *state;
>>>> + int order;
>>>> + int ret = 0;
>>>> +
>>>> + if (!str)
>>>> + goto out;
>>>> +
>>>> + size = (unsigned long)memparse(str, &state);
>>>> + order = ilog2(size >> PAGE_SHIFT);
>>>> + if (*state != ':' || !is_power_of_2(size) || size <= PAGE_SIZE ||
>>>> + !(BIT(order) & THP_ORDERS_ALL_ANON))
>>>> + goto out;
>>>> +
>>>> + state++;
>>>> +
>>>> + if (!strcmp(state, "always")) {
>>>> + clear_bit(order, &huge_anon_orders_inherit);
>>>> + clear_bit(order, &huge_anon_orders_madvise);
>>>> + set_bit(order, &huge_anon_orders_always);
>>>> + ret = 1;
>>>> + } else if (!strcmp(state, "inherit")) {
>>>> + clear_bit(order, &huge_anon_orders_always);
>>>> + clear_bit(order, &huge_anon_orders_madvise);
>>>> + set_bit(order, &huge_anon_orders_inherit);
>>>> + ret = 1;
>>>> + } else if (!strcmp(state, "madvise")) {
>>>> + clear_bit(order, &huge_anon_orders_always);
>>>> + clear_bit(order, &huge_anon_orders_inherit);
>>>> + set_bit(order, &huge_anon_orders_madvise);
>>>> + ret = 1;
>>>> + } else if (!strcmp(state, "never")) {
>>>> + clear_bit(order, &huge_anon_orders_always);
>>>> + clear_bit(order, &huge_anon_orders_inherit);
>>>> + clear_bit(order, &huge_anon_orders_madvise);
>>>> + ret = 1;
>>>> + }
>>>> +
>>>> + if (ret)
>>>> + anon_orders_configured = true;
>>>
>>> I mean:
>>>
>>> if (ret && order == PMD_ORDER)
>>> anon_pmd_order_configured = true;
>>>
>>>> +out:
>>>> + if (!ret)
>>>> + pr_warn("thp_anon=%s: cannot parse, ignored\n", str);
>>>> + return ret;
>>>> +}
>>>> +__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))
>>>> --
>>>> 2.43.0
>>>>
>>>
>>> Thanks
>>> Barry
>>
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