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Message-ID: <Yh/g2BRPZC3370mX@bombadil.infradead.org> 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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