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Message-ID: <ca3aaa3f-f018-46e4-aad1-c6a4fb8c7f11@redhat.com>
Date: Wed, 14 Aug 2024 10:18:44 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>, akpm@...ux-foundation.org,
linux-mm@...ck.org
Cc: baohua@...nel.org, baolin.wang@...ux.alibaba.com, corbet@....net,
ioworker0@...il.com, linux-kernel@...r.kernel.org, ryan.roberts@....com,
v-songbaohua@...o.com
Subject: Re: [PATCH v4] mm: Override mTHP "enabled" defaults at kernel cmdline
On 14.08.24 04:02, Barry Song wrote:
> From: Ryan Roberts <ryan.roberts@....com>
>
> 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>,<size>[KMG]:<value>;<size>-<size>[KMG]:<value>
>
> An example:
>
> thp_anon=16K-64K:always;128K,512K:inherit;256K:madvise;1M-2M:never
>
> 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>
> Co-developed-by: Barry Song <v-songbaohua@...o.com>
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> ---
> -v4:
> * use bitmap APIs to set and clear bits. thanks very much for
> David's comment!
>
> .../admin-guide/kernel-parameters.txt | 9 ++
> Documentation/admin-guide/mm/transhuge.rst | 37 +++++--
> mm/huge_memory.c | 96 ++++++++++++++++++-
> 3 files changed, 134 insertions(+), 8 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index f0057bac20fb..d0d141d50638 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6629,6 +6629,15 @@
> <deci-seconds>: poll all this frequency
> 0: no polling (default)
>
> + thp_anon= [KNL]
> + Format: <size>,<size>[KMG]:<state>;<size>-<size>[KMG]:<state>
> + state is one of "always", "madvise", "never" or "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 7072469de8a8..528e1a19d63f 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -284,13 +284,36 @@ that THP is shared. Exceeding the number would block the collapse::
>
> A higher value may increase memory footprint for some workloads.
>
> -Boot parameter
> -==============
> -
> -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.
> +Boot parameters
> +===============
> +
> +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>,<size>[KMG]:<state>;<size>-<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 16K, 32K, 64K THP to ``always``,
> +set 128K, 512K to ``inherit``, set 256K to ``madvise`` and 1M, 2M
> +to ``never``::
> +
> + thp_anon=16K-64K:always;128K,512K:inherit;256K:madvise;1M-2M:never
> +
> +``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``.
> +
> +``transparent_hugepage`` setting only affects the global toggle. If
> +``thp_anon`` is not specified, PMD_ORDER THP will default to ``inherit``.
> +However, if a valid ``thp_anon`` setting is provided by the user, the
> +PMD_ORDER THP policy will be overridden. If the policy for PMD_ORDER
> +is not defined within a valid ``thp_anon``, its policy will default to
> +``never``.
>
> Hugepages in tmpfs/shmem
> ========================
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 1a12c011e2df..c5f4e97b49de 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -81,6 +81,7 @@ 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,
> @@ -737,7 +738,10 @@ 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;
> + }
>
> *hugepage_kobj = kobject_create_and_add("transparent_hugepage", mm_kobj);
> if (unlikely(!*hugepage_kobj)) {
> @@ -922,6 +926,96 @@ static int __init setup_transparent_hugepage(char *str)
> }
> __setup("transparent_hugepage=", setup_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);
Do we have to also test if is_power_of_2(), and refuse if not? For
example, what if someone would pass 3K, would the existing check catch it?
> + order = fls(size >> PAGE_SHIFT) - 1;
Is this a fancy way of writing
order = log2(size >> PAGE_SHIFT);
? :)
Anyhow, if get_order() wraps that, all good.
> + if ((1 << order) & ~THP_ORDERS_ALL_ANON) {
> + pr_err("invalid size %s(order %d) in thp_anon boot parameter\n",
> + size_str, order);
> + return -EINVAL;
> + }
> +
> + return order;
> +}
Apart from that, nothing jumped at me.
--
Cheers,
David / dhildenb
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