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Biederman" , Andy Lutomirski , Sebastian Andrzej Siewior , "Liam R. Howlett" , Fenghua Yu , Andrei Vagin , Barret Rhoden , Michal Hocko , "Jason A. Donenfeld" , Alexey Gladkov , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Dinglan Peng , Pedro Fonseca , Jim Huang , Huichun Feng , Chih-En Lin Subject: [PATCH v4 05/14] mm/khugepaged: Break COW PTE before scanning pte Date: Tue, 7 Feb 2023 11:51:30 +0800 Message-Id: <20230207035139.272707-6-shiyn.lin@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230207035139.272707-1-shiyn.lin@gmail.com> References: <20230207035139.272707-1-shiyn.lin@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org We should not allow THP to collapse COW-ed PTE. So, break COW PTE before collapse_pte_mapped_thp() collapse to THP. Also, break COW PTE before khugepaged_scan_pmd() scan PTE. Signed-off-by: Chih-En Lin --- include/trace/events/huge_memory.h | 1 + mm/khugepaged.c | 35 +++++++++++++++++++++++++++++- 2 files changed, 35 insertions(+), 1 deletion(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 3e6fb05852f9..5f2c39f61521 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -13,6 +13,7 @@ EM( SCAN_PMD_NULL, "pmd_null") \ EM( SCAN_PMD_NONE, "pmd_none") \ EM( SCAN_PMD_MAPPED, "page_pmd_mapped") \ + EM( SCAN_COW_PTE, "cowed_pte") \ EM( SCAN_EXCEED_NONE_PTE, "exceed_none_pte") \ EM( SCAN_EXCEED_SWAP_PTE, "exceed_swap_pte") \ EM( SCAN_EXCEED_SHARED_PTE, "exceed_shared_pte") \ diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 90acfea40c13..1cddc20318d5 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -31,6 +31,7 @@ enum scan_result { SCAN_PMD_NULL, SCAN_PMD_NONE, SCAN_PMD_MAPPED, + SCAN_COW_PTE, SCAN_EXCEED_NONE_PTE, SCAN_EXCEED_SWAP_PTE, SCAN_EXCEED_SHARED_PTE, @@ -875,7 +876,7 @@ static int find_pmd_or_thp_or_none(struct mm_struct *mm, return SCAN_PMD_MAPPED; if (pmd_devmap(pmde)) return SCAN_PMD_NULL; - if (pmd_bad(pmde)) + if (pmd_write(pmde) && pmd_bad(pmde)) return SCAN_PMD_NULL; return SCAN_SUCCEED; } @@ -926,6 +927,8 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm, pte_unmap(vmf.pte); continue; } + if (break_cow_pte(vma, pmd, address)) + return SCAN_COW_PTE; ret = do_swap_page(&vmf); /* @@ -1038,6 +1041,9 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address, if (result != SCAN_SUCCEED) goto out_up_write; + /* We should already handled COW-ed PTE. */ + VM_WARN_ON(test_bit(MMF_COW_PTE, &mm->flags) && !pmd_write(*pmd)); + anon_vma_lock_write(vma->anon_vma); mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm, @@ -1148,6 +1154,13 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, memset(cc->node_load, 0, sizeof(cc->node_load)); nodes_clear(cc->alloc_nmask); + + /* Break COW PTE before we collapse the pages. */ + if (break_cow_pte(vma, pmd, address)) { + result = SCAN_COW_PTE; + goto out; + } + pte = pte_offset_map_lock(mm, pmd, address, &ptl); for (_address = address, _pte = pte; _pte < pte + HPAGE_PMD_NR; _pte++, _address += PAGE_SIZE) { @@ -1206,6 +1219,10 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm, goto out_unmap; } + /* + * If we only trigger the break COW PTE, the page usually + * still in COW mapping, which it still be shared. + */ if (page_mapcount(page) > 1) { ++shared; if (cc->is_khugepaged && @@ -1501,6 +1518,11 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, goto drop_hpage; } + /* We shouldn't let COW-ed PTE collapse. */ + if (break_cow_pte(vma, pmd, haddr)) + goto drop_hpage; + VM_WARN_ON(test_bit(MMF_COW_PTE, &mm->flags) && !pmd_write(*pmd)); + /* * We need to lock the mapping so that from here on, only GUP-fast and * hardware page walks can access the parts of the page tables that @@ -1706,6 +1728,11 @@ static int retract_page_tables(struct address_space *mapping, pgoff_t pgoff, result = SCAN_PTE_UFFD_WP; goto unlock_next; } + if (test_bit(MMF_COW_PTE, &mm->flags) && + !pmd_write(*pmd)) { + result = SCAN_COW_PTE; + goto unlock_next; + } collapse_and_free_pmd(mm, vma, addr, pmd); if (!cc->is_khugepaged && is_target) result = set_huge_pmd(vma, addr, pmd, hpage); @@ -2143,6 +2170,11 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, swap = 0; memset(cc->node_load, 0, sizeof(cc->node_load)); nodes_clear(cc->alloc_nmask); + if (break_cow_pte(find_vma(mm, addr), NULL, addr)) { + result = SCAN_COW_PTE; + goto out; + } + rcu_read_lock(); xas_for_each(&xas, page, start + HPAGE_PMD_NR - 1) { if (xas_retry(&xas, page)) @@ -2213,6 +2245,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, } rcu_read_unlock(); +out: if (result == SCAN_SUCCEED) { if (cc->is_khugepaged && present < HPAGE_PMD_NR - khugepaged_max_ptes_none) {