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Sun, 05 Jan 2025 19:17:28 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kernel@vger.kernel.org, ioworker0@gmail.com, david@redhat.com, ryan.roberts@arm.com, zhengtangquan@oppo.com, ying.huang@intel.com, kasong@tencent.com, chrisl@kernel.org, baolin.wang@linux.alibaba.com, Barry Song Subject: [PATCH 1/3] mm: set folio swapbacked iff folios are dirty in try_to_unmap_one Date: Mon, 6 Jan 2025 16:17:09 +1300 Message-Id: <20250106031711.82855-2-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250106031711.82855-1-21cnbao@gmail.com> References: <20250106031711.82855-1-21cnbao@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. Suggested-by: David Hildenbrand Signed-off-by: Barry Song --- mm/rmap.c | 49 ++++++++++++++++++++++--------------------------- 1 file changed, 22 insertions(+), 27 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index c6c4d4ea29a7..de6b8c34e98c 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1868,34 +1868,29 @@ static bool try_to_unmap_one(struct folio *folio, s= truct vm_area_struct *vma, */ smp_rmb(); =20 - /* - * The only page refs must be one from isolation - * plus the rmap(s) (dropped by discard:). - */ - if (ref_count =3D=3D 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 !=3D 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; } =20 if (swap_duplicate(entry) < 0) { --=20 2.39.3 (Apple Git-146)