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Message-ID: <axqj32jqs3ehzpz4vewtfbgcl2sg4lkntfm4prrqcd3evt7klr@qlurbuivkgbe>
Date: Mon, 22 Jul 2024 09:13:20 +0000
From: Daniel Gomez <da.gomez@...sung.com>
To: Ryan Roberts <ryan.roberts@....com>
CC: Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickins
<hughd@...gle.com>, Jonathan Corbet <corbet@....net>, "Matthew Wilcox
(Oracle)" <willy@...radead.org>, David Hildenbrand <david@...hat.com>,
"Barry Song" <baohua@...nel.org>, Lance Yang <ioworker0@...il.com>, Baolin
Wang <baolin.wang@...ux.alibaba.com>, Gavin Shan <gshan@...hat.com>, Pankaj
Raghav <kernel@...kajraghav.com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [RFC PATCH v1 3/4] mm: Override mTHP "enabled" defaults at
kernel cmdline
On Wed, Jul 17, 2024 at 08:12:55AM GMT, Ryan Roberts 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>
Minor suggestion. Should this be renamed to hp_anon= or hugepages_anon= instead?
This would align with the values under /sys/kernel/mm/transparent_hugepage/
hugepages-*kB.
>
> 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>
> ---
> .../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 bc55fb55cd26..48443ad12e3f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -6592,6 +6592,14 @@
> <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 1aaf8e3a0b5a..f53d43d986e2 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -311,13 +311,27 @@ performance.
> Note that any changes to the allowed set of sizes only applies to future
> file-backed THP allocations.
>
> -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 4249c0bc9388..794d2790d90d 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -82,6 +82,7 @@ unsigned long huge_anon_orders_madvise __read_mostly;
> unsigned long huge_anon_orders_inherit __read_mostly;
> unsigned long huge_file_orders_always __read_mostly;
> int huge_file_exec_order __read_mostly = -1;
> +static bool anon_orders_configured;
>
> unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
> unsigned long vm_flags,
> @@ -763,7 +764,10 @@ 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);
PMD_ORDER for 64k base PS systems would result in a 512M value, which exceeds
the xarray limit [1]. Therefore, I think we need to avoid PMD-size orders by
checking if PMD_ORDER > MAX_PAGECACHE_ORDER.
[1] https://lore.kernel.org/all/20240627003953.1262512-1-gshan@redhat.com/
> + anon_orders_configured = true;
> + }
>
> /*
> * For pagecache, default to enabling all orders. powerpc's PMD_ORDER
> @@ -955,6 +959,55 @@ 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;
> +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
>
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