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Fri, 14 Feb 2025 01:30:36 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, ioworker0@gmail.com, kasong@tencent.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com, ryan.roberts@arm.com, v-songbaohua@oppo.com, x86@kernel.org, ying.huang@intel.com, zhengtangquan@oppo.com, Mauricio Faria de Oliveira Subject: [PATCH v4 1/4] mm: Set folio swapbacked iff folios are dirty in try_to_unmap_one Date: Fri, 14 Feb 2025 22:30:12 +1300 Message-Id: <20250214093015.51024-2-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250214093015.51024-1-21cnbao@gmail.com> References: <20250214093015.51024-1-21cnbao@gmail.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250214_013038_176310_C8512B2E X-CRM114-Status: GOOD ( 14.90 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org From: Barry Song The refcount may be temporarily or long-term increased, but this does not change the fundamental nature of the folio already being lazy- freed. Therefore, we only reset 'swapbacked' when we are certain the folio is dirty and not droppable. Fixes: 6c8e2a256915 ("mm: fix race between MADV_FREE reclaim and blkdev direct IO read") Suggested-by: David Hildenbrand Signed-off-by: Barry Song Cc: Mauricio Faria de Oliveira Acked-by: David Hildenbrand Reviewed-by: Baolin Wang Reviewed-by: Lance Yang --- mm/rmap.c | 49 ++++++++++++++++++++++--------------------------- 1 file changed, 22 insertions(+), 27 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 25a8a127f689..1320527e90cd 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2022,34 +2022,29 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, */ smp_rmb(); - /* - * The only page refs must be one from isolation - * plus the rmap(s) (dropped by discard:). - */ - if (ref_count == 1 + map_count && - (!folio_test_dirty(folio) || - /* - * Unlike MADV_FREE mappings, VM_DROPPABLE - * ones can be dropped even if they've - * been dirtied. - */ - (vma->vm_flags & VM_DROPPABLE))) { - dec_mm_counter(mm, MM_ANONPAGES); - goto discard; - } - - /* - * If the folio was redirtied, it cannot be - * discarded. Remap the page to page table. - */ - set_pte_at(mm, address, pvmw.pte, pteval); - /* - * Unlike MADV_FREE mappings, VM_DROPPABLE ones - * never get swap backed on failure to drop. - */ - if (!(vma->vm_flags & VM_DROPPABLE)) + if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) { + /* + * redirtied either using the page table or a previously + * obtained GUP reference. + */ + set_pte_at(mm, address, pvmw.pte, pteval); folio_set_swapbacked(folio); - goto walk_abort; + goto walk_abort; + } else if (ref_count != 1 + map_count) { + /* + * Additional reference. Could be a GUP reference or any + * speculative reference. GUP users must mark the folio + * dirty if there was a modification. This folio cannot be + * reclaimed right now either way, so act just like nothing + * happened. + * We'll come back here later and detect if the folio was + * dirtied when the additional reference is gone. + */ + set_pte_at(mm, address, pvmw.pte, pteval); + goto walk_abort; + } + dec_mm_counter(mm, MM_ANONPAGES); + goto discard; } if (swap_duplicate(entry) < 0) {