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Date: Wed, 2 Mar 2022 13:25:44 -0800
From: Luis Chamberlain <mcgrof@...nel.org>
To: Muchun Song <songmuchun@...edance.com>
Cc: corbet@....net, mike.kravetz@...cle.com, akpm@...ux-foundation.org,
keescook@...omium.org, yzaikin@...gle.com,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, duanxiongchun@...edance.com, smuchun@...il.com,
Adam Manzanares <a.manzanares@...sung.com>,
Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH v2 3/3] mm: hugetlb: add hugetlb_free_vmemmap sysctl
On Wed, Mar 02, 2022 at 04:37:58PM +0800, Muchun Song wrote:
> We must add "hugetlb_free_vmemmap=on" to boot cmdline and reboot the
> server to enable the feature of freeing vmemmap pages of HugeTLB
> pages. Rebooting usually taske a long time. Add a sysctl to enable
> the feature at runtime and do not need to reboot.
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
> Documentation/admin-guide/sysctl/vm.rst | 13 ++++++++++
> include/linux/memory_hotplug.h | 9 +++++++
> mm/hugetlb_vmemmap.c | 42 ++++++++++++++++++++++++++++-----
> mm/hugetlb_vmemmap.h | 4 +++-
> mm/memory_hotplug.c | 5 ++++
> 5 files changed, 66 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index f4804ce37c58..01f18e6cc227 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -561,6 +561,19 @@ Change the minimum size of the hugepage pool.
> See Documentation/admin-guide/mm/hugetlbpage.rst
>
>
> +hugetlb_free_vmemmap
> +====================
> +
> +A toggle value indicating if vmemmap pages are allowed to be optimized.
> +If it is off (0), then it can be set true (1). Once true, the vmemmap
> +pages associated with each HugeTLB page will be optimized, and the toggle
> +cannot be set back to false. It only optimizes the subsequent allocation
> +of HugeTLB pages from buddy system, while already allocated HugeTLB pages
> +will not be optimized.
The commit log or documentation does not descrie why its safe to toggle
one way and not the other?
Luis
> +
> +See Documentation/admin-guide/mm/hugetlbpage.rst
> +
> +
> nr_hugepages_mempolicy
> ======================
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index e0b2209ab71c..20d7edf62a6a 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -351,4 +351,13 @@ void arch_remove_linear_mapping(u64 start, u64 size);
> extern bool mhp_supports_memmap_on_memory(unsigned long size);
> #endif /* CONFIG_MEMORY_HOTPLUG */
>
> +#ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> +bool mhp_memmap_on_memory(void);
> +#else
> +static inline bool mhp_memmap_on_memory(void)
> +{
> + return false;
> +}
> +#endif
> +
> #endif /* __LINUX_MEMORY_HOTPLUG_H */
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 836d1117f08b..3bcc8f25bd50 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -10,6 +10,7 @@
>
> #define pr_fmt(fmt) "HugeTLB: " fmt
>
> +#include <linux/memory_hotplug.h>
> #include "hugetlb_vmemmap.h"
>
> /*
> @@ -118,17 +119,14 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> BUILD_BUG_ON(__NR_USED_SUBPAGE >=
> RESERVE_VMEMMAP_SIZE / sizeof(struct page));
>
> - if (!hugetlb_free_vmemmap_enabled())
> - return;
> -
> - if (IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON) &&
> - !is_power_of_2(sizeof(struct page))) {
> + if (!is_power_of_2(sizeof(struct page))) {
> /*
> * The hugetlb_free_vmemmap_enabled_key can be enabled when
> * CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON. It should
> * be disabled if "struct page" crosses page boundaries.
> */
> - static_branch_disable(&hugetlb_free_vmemmap_enabled_key);
> + if (IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON))
> + static_branch_disable(&hugetlb_free_vmemmap_enabled_key);
> return;
> }
>
> @@ -147,3 +145,35 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
> pr_info("can free %d vmemmap pages for %s\n", h->nr_free_vmemmap_pages,
> h->name);
> }
> +
> +static struct ctl_table hugetlb_vmemmap_sysctls[] = {
> + {
> + .procname = "hugetlb_free_vmemmap",
> + .data = &hugetlb_free_vmemmap_enabled_key.key,
> + .mode = 0644,
> + /* only handle a transition from default "0" to "1" */
> + .proc_handler = proc_do_static_key,
> + .extra1 = SYSCTL_ONE,
> + .extra2 = SYSCTL_ONE,
> + },
> + { }
> +};
> +
> +static __init int hugetlb_vmemmap_sysctls_init(void)
> +{
> + /*
> + * The vmemmap pages cannot be optimized if
> + * "memory_hotplug.memmap_on_memory" is enabled unless
> + * "hugetlb_free_vmemmap" is enabled as well since
> + * "hugetlb_free_vmemmap" takes precedence over
> + * "memory_hotplug.memmap_on_memory".
> + */
> + if (mhp_memmap_on_memory() && !hugetlb_free_vmemmap_enabled())
> + return 0;
> +
> + if (is_power_of_2(sizeof(struct page)))
> + register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
> +
> + return 0;
> +}
> +late_initcall(hugetlb_vmemmap_sysctls_init);
> diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
> index cb2bef8f9e73..b67a159027f4 100644
> --- a/mm/hugetlb_vmemmap.h
> +++ b/mm/hugetlb_vmemmap.h
> @@ -21,7 +21,9 @@ void hugetlb_vmemmap_init(struct hstate *h);
> */
> static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
> {
> - return h->nr_free_vmemmap_pages;
> + if (hugetlb_free_vmemmap_enabled())
> + return h->nr_free_vmemmap_pages;
> + return 0;
> }
> #else
> static inline int alloc_huge_page_vmemmap(struct hstate *h, struct page *head)
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index c226a337c1ef..c2115e566abc 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -50,6 +50,11 @@ static bool memmap_on_memory __ro_after_init;
> #ifdef CONFIG_MHP_MEMMAP_ON_MEMORY
> module_param(memmap_on_memory, bool, 0444);
> MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
> +
> +bool mhp_memmap_on_memory(void)
> +{
> + return memmap_on_memory;
> +}
> #endif
>
> enum {
> --
> 2.11.0
>
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