When the size of a struct page is not multiple of 2MB, sections do not span a PMD anymore and so when populating them some parts of the PMD will remain unused. Because of this, PMDs will be left behind when depopulating sections since remove_pmd_table() thinks that those unused parts are still in use.
Fix this by marking the unused parts with PAGE_INUSE, so memchr_inv() will do the right thing and will let us free the PMD when the last user of it is gone. This patch is based on a similar patch by David Hildenbrand: https://lore.kernel.org/linux-mm/20200722094558.9828-9-da...@redhat.com/ https://lore.kernel.org/linux-mm/20200722094558.9828-10-da...@redhat.com/ Signed-off-by: Oscar Salvador <osalva...@suse.de> --- v1 -> v2: - Rename PAGE_INUSE to PAGE_UNUSED as it better describes what we do --- arch/x86/mm/init_64.c | 91 +++++++++++++++++++++++++++++++++++++------ 1 file changed, 79 insertions(+), 12 deletions(-) diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index b5a3fa4033d3..dbb76160ed52 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -871,7 +871,72 @@ int arch_add_memory(int nid, u64 start, u64 size, return add_pages(nid, start_pfn, nr_pages, params); } -#define PAGE_INUSE 0xFD +#define PAGE_UNUSED 0xFD + +/* + * The unused vmemmap range, which was not yet memset(PAGE_UNUSED) ranges + * from unused_pmd_start to next PMD_SIZE boundary. + */ +static unsigned long unused_pmd_start __meminitdata; + +static void __meminit vmemmap_flush_unused_pmd(void) +{ + if (!unused_pmd_start) + return; + /* + * Clears (unused_pmd_start, PMD_END] + */ + memset((void *)unused_pmd_start, PAGE_UNUSED, + ALIGN(unused_pmd_start, PMD_SIZE) - unused_pmd_start); + unused_pmd_start = 0; +} + +/* Returns true if the PMD is completely unused and thus it can be freed */ +static bool __meminit vmemmap_unuse_sub_pmd(unsigned long addr, unsigned long end) +{ + unsigned long start = ALIGN_DOWN(addr, PMD_SIZE); + + vmemmap_flush_unused_pmd(); + memset((void *)addr, PAGE_UNUSED, end - addr); + + return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE); +} + +static void __meminit vmemmap_use_sub_pmd(unsigned long start, unsigned long end) +{ + /* + * We only optimize if the new used range directly follows the + * previously unused range (esp., when populating consecutive sections). + */ + if (unused_pmd_start == start) { + if (likely(IS_ALIGNED(end, PMD_SIZE))) + unused_pmd_start = 0; + else + unused_pmd_start = end; + return; + } + + vmemmap_flush_unused_pmd(); +} + +static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end) +{ + vmemmap_flush_unused_pmd(); + + /* + * Mark the unused parts of the new memmap range + */ + if (!IS_ALIGNED(start, PMD_SIZE)) + memset((void *)start, PAGE_UNUSED, + start - ALIGN_DOWN(start, PMD_SIZE)); + /* + * We want to avoid memset(PAGE_UNUSED) when populating the vmemmap of + * consecutive sections. Remember for the last added PMD the last + * unused range in the populated PMD. + */ + if (!IS_ALIGNED(end, PMD_SIZE)) + unused_pmd_start = end; +} static void __meminit free_pagetable(struct page *page, int order) { @@ -1008,10 +1073,10 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end, * with 0xFD, and remove the page when it is wholly * filled with 0xFD. */ - memset((void *)addr, PAGE_INUSE, next - addr); + memset((void *)addr, PAGE_UNUSED, next - addr); page_addr = page_address(pte_page(*pte)); - if (!memchr_inv(page_addr, PAGE_INUSE, PAGE_SIZE)) { + if (!memchr_inv(page_addr, PAGE_UNUSED, PAGE_SIZE)) { free_pagetable(pte_page(*pte), 0); spin_lock(&init_mm.page_table_lock); @@ -1034,7 +1099,6 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, unsigned long next, pages = 0; pte_t *pte_base; pmd_t *pmd; - void *page_addr; pmd = pmd_start + pmd_index(addr); for (; addr < end; addr = next, pmd++) { @@ -1055,12 +1119,10 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, spin_unlock(&init_mm.page_table_lock); pages++; } else { - /* If here, we are freeing vmemmap pages. */ - memset((void *)addr, PAGE_INUSE, next - addr); - - page_addr = page_address(pmd_page(*pmd)); - if (!memchr_inv(page_addr, PAGE_INUSE, - PMD_SIZE)) { + /* + * Free the PMD if the whole range is unused. + */ + if (vmemmap_unuse_sub_pmd(addr, next)) { free_hugepage_table(pmd_page(*pmd), altmap); @@ -1112,10 +1174,10 @@ remove_pud_table(pud_t *pud_start, unsigned long addr, unsigned long end, pages++; } else { /* If here, we are freeing vmemmap pages. */ - memset((void *)addr, PAGE_INUSE, next - addr); + memset((void *)addr, PAGE_UNUSED, next - addr); page_addr = page_address(pud_page(*pud)); - if (!memchr_inv(page_addr, PAGE_INUSE, + if (!memchr_inv(page_addr, PAGE_UNUSED, PUD_SIZE)) { free_pagetable(pud_page(*pud), get_order(PUD_SIZE)); @@ -1538,11 +1600,16 @@ static int __meminit vmemmap_populate_hugepages(unsigned long start, addr_end = addr + PMD_SIZE; p_end = p + PMD_SIZE; + + if (!IS_ALIGNED(addr, PMD_SIZE) || + !IS_ALIGNED(next, PMD_SIZE)) + vmemmap_use_new_sub_pmd(addr, next); continue; } else if (altmap) return -ENOMEM; /* no fallback */ } else if (pmd_large(*pmd)) { vmemmap_verify((pte_t *)pmd, node, addr, next); + vmemmap_use_sub_pmd(addr, next); continue; } if (vmemmap_populate_basepages(addr, next, node, NULL)) -- 2.26.2
