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Message-ID: <fe784034-0321-481b-96c0-ac5c48e0fb84@arm.com>
Date: Fri, 9 Aug 2024 08:58:29 +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 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?
>
>>
>> *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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