From d8d55f5616cf3b900a23a72dd24e7b07211e7859 Mon Sep 17 00:00:00 2001 From: Muchun Song Date: Tue, 22 Mar 2022 14:45:06 -0700 Subject: mm: sparsemem: use page table lock to protect kernel pmd operations The init_mm.page_table_lock is used to protect kernel page tables, we can use it to serialize splitting vmemmap PMD mappings instead of mmap write lock, which can increase the concurrency of vmemmap_remap_free(). Actually, It increase the concurrency between allocations of HugeTLB pages. But it is not the only benefit. There are a lot of users of mmap read lock of init_mm. The mmap write lock is holding through vmemmap_remap_free(), removing mmap write lock usage to make it does not affect other users of mmap read lock. It is not making anything worse and always a win to move. Now the kernel page table walker does not hold the page_table_lock when walking pmd entries. There may be consistency issue of a pmd entry, because pmd entry might change from a huge pmd entry to a PTE page table. There is only one user of kernel page table walker, namely ptdump. The ptdump already considers the consistency, which use a local variable to cache the value of pmd entry. But we also need to update ->action to ACTION_CONTINUE to make sure the walker does not walk every pte entry again when concurrent thread has split the huge pmd. Link: https://lkml.kernel.org/r/20211101031651.75851-4-songmuchun@bytedance.com Signed-off-by: Muchun Song Cc: Barry Song Cc: Bodeddula Balasubramaniam Cc: Chen Huang Cc: David Hildenbrand Cc: Fam Zheng Cc: Jonathan Corbet Cc: Matthew Wilcox Cc: Michal Hocko Cc: Mike Kravetz Cc: Oscar Salvador Cc: Qi Zheng Cc: Xiongchun Duan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/ptdump.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) (limited to 'mm/ptdump.c') diff --git a/mm/ptdump.c b/mm/ptdump.c index da751448d0e4..eea3d28d173c 100644 --- a/mm/ptdump.c +++ b/mm/ptdump.c @@ -40,8 +40,10 @@ static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr, if (st->effective_prot) st->effective_prot(st, 0, pgd_val(val)); - if (pgd_leaf(val)) + if (pgd_leaf(val)) { st->note_page(st, addr, 0, pgd_val(val)); + walk->action = ACTION_CONTINUE; + } return 0; } @@ -61,8 +63,10 @@ static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr, if (st->effective_prot) st->effective_prot(st, 1, p4d_val(val)); - if (p4d_leaf(val)) + if (p4d_leaf(val)) { st->note_page(st, addr, 1, p4d_val(val)); + walk->action = ACTION_CONTINUE; + } return 0; } @@ -82,8 +86,10 @@ static int ptdump_pud_entry(pud_t *pud, unsigned long addr, if (st->effective_prot) st->effective_prot(st, 2, pud_val(val)); - if (pud_leaf(val)) + if (pud_leaf(val)) { st->note_page(st, addr, 2, pud_val(val)); + walk->action = ACTION_CONTINUE; + } return 0; } @@ -101,8 +107,10 @@ static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr, if (st->effective_prot) st->effective_prot(st, 3, pmd_val(val)); - if (pmd_leaf(val)) + if (pmd_leaf(val)) { st->note_page(st, addr, 3, pmd_val(val)); + walk->action = ACTION_CONTINUE; + } return 0; } -- cgit v1.2.3