On 20.06.22 09:22, Muchun Song wrote: > On Sun, Jun 19, 2022 at 09:38:51PM +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@xxxxxxxxxxxxx> >> Co-developed-by: Oscar Salvador <osalvador@xxxxxxx> >> Signed-off-by: Oscar Salvador <osalvador@xxxxxxx> >> --- >> Documentation/admin-guide/kernel-parameters.txt | 22 +++++------ >> Documentation/admin-guide/sysctl/vm.rst | 5 +-- >> include/linux/memory_hotplug.h | 9 ----- >> include/linux/page-flags.h | 11 ++++++ >> mm/hugetlb_vmemmap.c | 52 +++++++++++++++++++++---- >> mm/memory_hotplug.c | 27 ++++++------- >> 6 files changed, 79 insertions(+), 47 deletions(-) >> >> 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..73bfbb47f6a4 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 +97,54 @@ 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)) { >> + unsigned long pfn = page_to_pfn(head); >> + >> + /* >> + * 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 the first >> + * vmemmap page's vmemmap if it is marked as VmemmapSelfHosted >> + * is sufficient. >> + * >> + * [ hotplugged memory ] >> + * [ section ][...][ section ] >> + * [ vmemmap ][ usable memory ] >> + * ^ | | | >> + * +---+ | | >> + * ^ | | >> + * +-------+ | >> + * ^ | >> + * +-------------------------------------------+ >> + * >> + * Hotplugged memory block never has non-present sections, while >> + * boot memory block can have one or more. So pfn_valid() is >> + * used to filter out the non-present section which also cannot >> + * be memmap_on_memory. >> + */ >> + pfn = ALIGN_DOWN(pfn, PHYS_PFN(memory_block_size_bytes())); >> + if (pfn_valid(pfn) && PageVmemmapSelfHosted(pfn_to_page(pfn))) > > Although it works, I think PageVmemmapSelfHosted() check for the 1st pfn's > vmemmap page is not always reliable. Since we reused PG_owner_priv_1 > as PG_vmemmap_self_hosted, the test is noly reliable for vmemmap page's > vmemmap page. Other non-vmemmap page can be flagged with PG_owner_priv_1. > So this check can be false-positive. Maybe the following code snippet is > the solution. How could that happen for pages used for backing a vmemmap? > > Any thoughts? Oscar or David. First of all, I think you should really avoid using memory_block_size_bytes(); when using memory_block_size_bytes(), you wouldn't need PageVmemmapSelfHosted(), you can just check if the vmemmap of the page is itself. But I think we should try making this independent of the memory block size. If virt_to_page(page) doesn't work, maybe just traverse the direct map to find the page backing page directly? -- Thanks, David / dhildenb