| Message ID | 20220620110616.12056-3-songmuchun@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | make hugetlb_optimize_vmemmap compatible with memmap_on_memory | expand |
On Mon, Jun 20, 2022 at 07:06:16PM +0800, Muchun Song wrote: > + /* > + * The READ_ONCE() is used to stabilize *pmdp in a register or > + * on the stack so that it will stop changing under the code. > + * The only concurrent operation where it can be changed is > + * split_vmemmap_huge_pmd() (*pmdp will be stable after this > + * operation). > + */ > + pmd = READ_ONCE(*pmdp); > + if (pmd_leaf(pmd)) > + vmemmap_page = pmd_page(pmd) + pte_index(vaddr); > + else > + vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr)); I was about to suggest to get rid of the else branch because on x86_64 we can only allocate PMD_SIZE chunks when using an alternative allocator, meaning that anything which is not a pmd_leaf can't be a PageVmemmapSelfHosted. But then I went to check the other platform that supports memmap_on_memory (arm64), and in there I can see that we fallback to populate basepages with altmap should we fail to allocate a PMD_SIZE chunk. > + /* > + * Due to HugeTLB alignment requirements and the vmemmap pages > + * being at the start of the hotplugged memory region in > + * memory_hotplug.memmap_on_memory case. Checking any vmemmap > + * page's vmemmap page if it is marked as VmemmapSelfHosted is > + * sufficient. > + * > + * [ hotplugged memory ] > + * [ section ][...][ section ] > + * [ vmemmap ][ usable memory ] > + * ^ | | | > + * +---+ | | > + * ^ | | > + * +-------+ | > + * ^ | > + * +-------------------------------------------+ > + */ > + if (PageVmemmapSelfHosted(vmemmap_page)) > + return 0; > + } > + > + return hugetlb_optimize_vmemmap_pages(h); > +} > + > void hugetlb_vmemmap_free(struct hstate *h, struct page *head) > { > unsigned long vmemmap_addr = (unsigned long)head; > unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages; > > - vmemmap_pages = hugetlb_optimize_vmemmap_pages(h); > + vmemmap_pages = vmemmap_optimizable_pages(h, head); > if (!vmemmap_pages) > return; > > - if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF) > - return; > - > static_branch_inc(&hugetlb_optimize_vmemmap_key); > > vmemmap_addr += RESERVE_VMEMMAP_SIZE; > @@ -199,10 +249,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = { > static __init int hugetlb_vmemmap_sysctls_init(void) > { > /* > - * If "memory_hotplug.memmap_on_memory" is enabled or "struct page" > - * crosses page boundaries, the vmemmap pages cannot be optimized. > + * If "struct page" crosses page boundaries, the vmemmap pages cannot > + * be optimized. > */ > - if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page))) > + if (is_power_of_2(sizeof(struct page))) > register_sysctl_init("vm", hugetlb_vmemmap_sysctls); > > return 0; > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 6662b86e9e64..3a59d4e97c03 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -43,30 +43,22 @@ > #include "shuffle.h" > > #ifdef CONFIG_MHP_MEMMAP_ON_MEMORY > -static int memmap_on_memory_set(const char *val, const struct kernel_param *kp) > -{ > - if (hugetlb_optimize_vmemmap_enabled()) > - return 0; > - return param_set_bool(val, kp); > -} > - > -static const struct kernel_param_ops memmap_on_memory_ops = { > - .flags = KERNEL_PARAM_OPS_FL_NOARG, > - .set = memmap_on_memory_set, > - .get = param_get_bool, > -}; > - > /* > * memory_hotplug.memmap_on_memory parameter > */ > static bool memmap_on_memory __ro_after_init; > -module_param_cb(memmap_on_memory, &memmap_on_memory_ops, &memmap_on_memory, 0444); > +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) > +static inline bool mhp_memmap_on_memory(void) > { > return memmap_on_memory; > } > +#else > +static inline bool mhp_memmap_on_memory(void) > +{ > + return false; > +} > #endif > > enum { > @@ -1035,7 +1027,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages, > struct zone *zone) > { > unsigned long end_pfn = pfn + nr_pages; > - int ret; > + int ret, i; > > ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages)); > if (ret) > @@ -1043,6 +1035,9 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages, > > move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE); > > + for (i = 0; i < nr_pages; i++) > + SetPageVmemmapSelfHosted(pfn_to_page(pfn + i)); > + > /* > * It might be that the vmemmap_pages fully span sections. If that is > * the case, mark those sections online here as otherwise they will be > -- > 2.11.0 > >
On Mon, Jun 20, 2022 at 03:19:33PM +0200, Oscar Salvador wrote: > On Mon, Jun 20, 2022 at 07:06:16PM +0800, Muchun Song wrote: > > + /* > > + * The READ_ONCE() is used to stabilize *pmdp in a register or > > + * on the stack so that it will stop changing under the code. > > + * The only concurrent operation where it can be changed is > > + * split_vmemmap_huge_pmd() (*pmdp will be stable after this > > + * operation). > > + */ > > + pmd = READ_ONCE(*pmdp); > > + if (pmd_leaf(pmd)) > > + vmemmap_page = pmd_page(pmd) + pte_index(vaddr); > > + else > > + vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr)); > > I was about to suggest to get rid of the else branch because on x86_64 > we can only allocate PMD_SIZE chunks when using an alternative allocator, > meaning that anything which is not a pmd_leaf can't be a PageVmemmapSelfHosted. > You are right. However, I think relaying on this condition is fragile and not straightforward compared to the check of PageVmemmapSelfHosted(). And the else branch is not in a hot path. So I'd like to stay with it. Does this make sense for you? > But then I went to check the other platform that supports memmap_on_memory (arm64), > and in there I can see that we fallback to populate basepages with altmap should > we fail to allocate a PMD_SIZE chunk. > I think it cannot be fail for memmap_on_memory case. Thanks.
On 20.06.22 13:06, Muchun Song wrote: > For now, the feature of hugetlb_free_vmemmap is not compatible with the > feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap > takes precedence over memory_hotplug.memmap_on_memory. However, someone > wants to make memory_hotplug.memmap_on_memory takes precedence over > hugetlb_free_vmemmap since memmap_on_memory makes it more likely to > succeed memory hotplug in close-to-OOM situations. So the decision > of making hugetlb_free_vmemmap take precedence is not wise and elegant. > The proper approach is to have hugetlb_vmemmap.c do the check whether > the section which the HugeTLB pages belong to can be optimized. If > the section's vmemmap pages are allocated from the added memory block > itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap, > otherwise, do the optimization. Then both kernel parameters are > compatible. So this patch introduces VmemmapSelfHosted to mask any > non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag > to detect if a vmemmap page can be optimized. > Makes sense to me and looks good Acked-by: David Hildenbrand <david@redhat.com>
On Mon, Jun 20, 2022 at 07:06:16PM +0800, Muchun Song wrote: > For now, the feature of hugetlb_free_vmemmap is not compatible with the > feature of memory_hotplug.memmap_on_memory, and hugetlb_free_vmemmap > takes precedence over memory_hotplug.memmap_on_memory. However, someone > wants to make memory_hotplug.memmap_on_memory takes precedence over > hugetlb_free_vmemmap since memmap_on_memory makes it more likely to > succeed memory hotplug in close-to-OOM situations. So the decision > of making hugetlb_free_vmemmap take precedence is not wise and elegant. > The proper approach is to have hugetlb_vmemmap.c do the check whether > the section which the HugeTLB pages belong to can be optimized. If > the section's vmemmap pages are allocated from the added memory block > itself, hugetlb_free_vmemmap should refuse to optimize the vmemmap, > otherwise, do the optimization. Then both kernel parameters are > compatible. So this patch introduces VmemmapSelfHosted to mask any > non-optimizable vmemmap pages. The hugetlb_vmemmap can use this flag > to detect if a vmemmap page can be optimized. > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > Co-developed-by: Oscar Salvador <osalvador@suse.de> > Signed-off-by: Oscar Salvador <osalvador@suse.de> LGTM, thanks for working on this!
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 8090130b544b..d740e2ed0e61 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1722,9 +1722,11 @@ Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, the default is on. - This is not compatible with memory_hotplug.memmap_on_memory. - If both parameters are enabled, hugetlb_free_vmemmap takes - precedence over memory_hotplug.memmap_on_memory. + Note that the vmemmap pages may be allocated from the added + memory block itself when memory_hotplug.memmap_on_memory is + enabled, those vmemmap pages cannot be optimized even if this + feature is enabled. Other vmemmap pages not allocated from + the added memory block itself do not be affected. hung_task_panic= [KNL] Should the hung task detector generate panics. @@ -3069,10 +3071,12 @@ [KNL,X86,ARM] Boolean flag to enable this feature. Format: {on | off (default)} When enabled, runtime hotplugged memory will - allocate its internal metadata (struct pages) - from the hotadded memory which will allow to - hotadd a lot of memory without requiring - additional memory to do so. + allocate its internal metadata (struct pages, + those vmemmap pages cannot be optimized even + if hugetlb_free_vmemmap is enabled) from the + hotadded memory which will allow to hotadd a + lot of memory without requiring additional + memory to do so. This feature is disabled by default because it has some implication on large (e.g. GB) allocations in some configurations (e.g. small @@ -3082,10 +3086,6 @@ Note that even when enabled, there are a few cases where the feature is not effective. - This is not compatible with hugetlb_free_vmemmap. If - both parameters are enabled, hugetlb_free_vmemmap takes - precedence over memory_hotplug.memmap_on_memory. - memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest Format: <integer> default : 0 <disable> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index 5c9aa171a0d3..d7374a1e8ac9 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -565,9 +565,8 @@ See Documentation/admin-guide/mm/hugetlbpage.rst hugetlb_optimize_vmemmap ======================== -This knob is not available when memory_hotplug.memmap_on_memory (kernel parameter) -is configured or the size of 'struct page' (a structure defined in -include/linux/mm_types.h) is not power of two (an unusual system config could +This knob is not available when the size of 'struct page' (a structure defined +in include/linux/mm_types.h) is not power of two (an unusual system config could result in this). Enable (set to 1) or disable (set to 0) the feature of optimizing vmemmap pages diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h index 20d7edf62a6a..e0b2209ab71c 100644 --- a/include/linux/memory_hotplug.h +++ b/include/linux/memory_hotplug.h @@ -351,13 +351,4 @@ 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/include/linux/page-flags.h b/include/linux/page-flags.h index e66f7aa3191d..2aa5dcbfe468 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -193,6 +193,11 @@ enum pageflags { /* Only valid for buddy pages. Used to track pages that are reported */ PG_reported = PG_uptodate, + +#ifdef CONFIG_MEMORY_HOTPLUG + /* For self-hosted memmap pages */ + PG_vmemmap_self_hosted = PG_owner_priv_1, +#endif }; #define PAGEFLAGS_MASK ((1UL << NR_PAGEFLAGS) - 1) @@ -628,6 +633,12 @@ PAGEFLAG_FALSE(SkipKASanPoison, skip_kasan_poison) */ __PAGEFLAG(Reported, reported, PF_NO_COMPOUND) +#ifdef CONFIG_MEMORY_HOTPLUG +PAGEFLAG(VmemmapSelfHosted, vmemmap_self_hosted, PF_ANY) +#else +PAGEFLAG_FALSE(VmemmapSelfHosted, vmemmap_self_hosted) +#endif + /* * On an anonymous page mapped into a user virtual memory area, * page->mapping points to its anon_vma, not to a struct address_space; diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c index 1089ea8a9c98..6d9801bb3fec 100644 --- a/mm/hugetlb_vmemmap.c +++ b/mm/hugetlb_vmemmap.c @@ -10,7 +10,7 @@ */ #define pr_fmt(fmt) "HugeTLB: " fmt -#include <linux/memory_hotplug.h> +#include <linux/memory.h> #include "hugetlb_vmemmap.h" /* @@ -97,18 +97,68 @@ int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head) return ret; } +static unsigned int vmemmap_optimizable_pages(struct hstate *h, + struct page *head) +{ + if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF) + return 0; + + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) { + pmd_t *pmdp, pmd; + struct page *vmemmap_page; + unsigned long vaddr = (unsigned long)head; + + /* + * Only the vmemmap page's vmemmap page can be self-hosted. + * Walking the page tables to find the backing page of the + * vmemmap page. + */ + pmdp = pmd_off_k(vaddr); + /* + * The READ_ONCE() is used to stabilize *pmdp in a register or + * on the stack so that it will stop changing under the code. + * The only concurrent operation where it can be changed is + * split_vmemmap_huge_pmd() (*pmdp will be stable after this + * operation). + */ + pmd = READ_ONCE(*pmdp); + if (pmd_leaf(pmd)) + vmemmap_page = pmd_page(pmd) + pte_index(vaddr); + else + vmemmap_page = pte_page(*pte_offset_kernel(pmdp, vaddr)); + /* + * Due to HugeTLB alignment requirements and the vmemmap pages + * being at the start of the hotplugged memory region in + * memory_hotplug.memmap_on_memory case. Checking any vmemmap + * page's vmemmap page if it is marked as VmemmapSelfHosted is + * sufficient. + * + * [ hotplugged memory ] + * [ section ][...][ section ] + * [ vmemmap ][ usable memory ] + * ^ | | | + * +---+ | | + * ^ | | + * +-------+ | + * ^ | + * +-------------------------------------------+ + */ + if (PageVmemmapSelfHosted(vmemmap_page)) + return 0; + } + + return hugetlb_optimize_vmemmap_pages(h); +} + void hugetlb_vmemmap_free(struct hstate *h, struct page *head) { unsigned long vmemmap_addr = (unsigned long)head; unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages; - vmemmap_pages = hugetlb_optimize_vmemmap_pages(h); + vmemmap_pages = vmemmap_optimizable_pages(h, head); if (!vmemmap_pages) return; - if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF) - return; - static_branch_inc(&hugetlb_optimize_vmemmap_key); vmemmap_addr += RESERVE_VMEMMAP_SIZE; @@ -199,10 +249,10 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = { static __init int hugetlb_vmemmap_sysctls_init(void) { /* - * If "memory_hotplug.memmap_on_memory" is enabled or "struct page" - * crosses page boundaries, the vmemmap pages cannot be optimized. + * If "struct page" crosses page boundaries, the vmemmap pages cannot + * be optimized. */ - if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page))) + if (is_power_of_2(sizeof(struct page))) register_sysctl_init("vm", hugetlb_vmemmap_sysctls); return 0; diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 6662b86e9e64..3a59d4e97c03 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -43,30 +43,22 @@ #include "shuffle.h" #ifdef CONFIG_MHP_MEMMAP_ON_MEMORY -static int memmap_on_memory_set(const char *val, const struct kernel_param *kp) -{ - if (hugetlb_optimize_vmemmap_enabled()) - return 0; - return param_set_bool(val, kp); -} - -static const struct kernel_param_ops memmap_on_memory_ops = { - .flags = KERNEL_PARAM_OPS_FL_NOARG, - .set = memmap_on_memory_set, - .get = param_get_bool, -}; - /* * memory_hotplug.memmap_on_memory parameter */ static bool memmap_on_memory __ro_after_init; -module_param_cb(memmap_on_memory, &memmap_on_memory_ops, &memmap_on_memory, 0444); +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) +static inline bool mhp_memmap_on_memory(void) { return memmap_on_memory; } +#else +static inline bool mhp_memmap_on_memory(void) +{ + return false; +} #endif enum { @@ -1035,7 +1027,7 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages, struct zone *zone) { unsigned long end_pfn = pfn + nr_pages; - int ret; + int ret, i; ret = kasan_add_zero_shadow(__va(PFN_PHYS(pfn)), PFN_PHYS(nr_pages)); if (ret) @@ -1043,6 +1035,9 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages, move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE); + for (i = 0; i < nr_pages; i++) + SetPageVmemmapSelfHosted(pfn_to_page(pfn + i)); + /* * It might be that the vmemmap_pages fully span sections. If that is * the case, mark those sections online here as otherwise they will be