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Howlett" , David Hildenbrand , Vlastimil Babka , Jann Horn , Suren Baghdasaryan , Lokesh Gidra , Mike Rapoport , Michal Hocko , Tangquan Zheng , Qi Zheng Subject: [PATCH RFC] mm: madvise: use per_vma lock for MADV_FREE Date: Tue, 10 Jun 2025 17:59:20 +1200 Message-Id: <20250610055920.21323-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable From: Barry Song MADV_FREE is another option, besides MADV_DONTNEED, for dynamic memory freeing in user-space native or Java heap memory management. For example, jemalloc can be configured to use MADV_FREE, and recent versions of the Android Java heap have also increasingly adopted MADV_FREE. Supporting per-VMA locking for MADV_FREE thus appears increasingly necessary. We have replaced walk_page_range() with walk_page_range_vma(). Along with the proposed madvise_lock_mode by Lorenzo, the necessary infrastructure is now in place to begin exploring per-VMA locking support for MADV_FREE and potentially other madvise using walk_page_range_vma(). This patch adds support for the PGWALK_VMA_RDLOCK walk_lock mode in walk_page_range_vma(), and leverages madvise_lock_mode from madv_behavior to select the appropriate walk_lock=E2=80=94either mmap_lock = or per-VMA lock=E2=80=94based on the context. To ensure thread safety, madvise_free_walk_ops is now defined as a stack variable instead of a global constant. Cc: Lorenzo Stoakes Cc: "Liam R. Howlett" Cc: David Hildenbrand Cc: Vlastimil Babka Cc: Jann Horn Cc: Suren Baghdasaryan Cc: Lokesh Gidra Cc: Mike Rapoport Cc: Michal Hocko Cc: Tangquan Zheng Cc: Qi Zheng Signed-off-by: Barry Song Acked-by: David Hildenbrand Reviewed-by: Lorenzo Stoakes --- include/linux/pagewalk.h | 2 ++ mm/madvise.c | 20 ++++++++++++++------ mm/pagewalk.c | 6 ++++++ 3 files changed, 22 insertions(+), 6 deletions(-) diff --git a/include/linux/pagewalk.h b/include/linux/pagewalk.h index 9700a29f8afb..a4afa64ef0ab 100644 --- a/include/linux/pagewalk.h +++ b/include/linux/pagewalk.h @@ -14,6 +14,8 @@ enum page_walk_lock { PGWALK_WRLOCK =3D 1, /* vma is expected to be already write-locked during the walk */ PGWALK_WRLOCK_VERIFY =3D 2, + /* vma is expected to be already read-locked during the walk */ + PGWALK_VMA_RDLOCK_VERIFY =3D 3, }; =20 /** diff --git a/mm/madvise.c b/mm/madvise.c index 381eedde8f6d..23d58eb31c8f 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -775,10 +775,14 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigne= d long addr, return 0; } =20 -static const struct mm_walk_ops madvise_free_walk_ops =3D { - .pmd_entry =3D madvise_free_pte_range, - .walk_lock =3D PGWALK_RDLOCK, -}; +static inline enum page_walk_lock get_walk_lock(enum madvise_lock_mode mod= e) +{ + /* Other modes don't require fixing up the walk_lock. */ + VM_WARN_ON_ONCE(mode !=3D MADVISE_VMA_READ_LOCK && + mode !=3D MADVISE_MMAP_READ_LOCK); + return mode =3D=3D MADVISE_VMA_READ_LOCK ? + PGWALK_VMA_RDLOCK_VERIFY : PGWALK_RDLOCK; +} =20 static int madvise_free_single_vma(struct madvise_behavior *madv_behavior, struct vm_area_struct *vma, @@ -787,6 +791,9 @@ static int madvise_free_single_vma(struct madvise_behav= ior *madv_behavior, struct mm_struct *mm =3D vma->vm_mm; struct mmu_notifier_range range; struct mmu_gather *tlb =3D madv_behavior->tlb; + struct mm_walk_ops walk_ops =3D { + .pmd_entry =3D madvise_free_pte_range, + }; =20 /* MADV_FREE works for only anon vma at the moment */ if (!vma_is_anonymous(vma)) @@ -806,8 +813,9 @@ static int madvise_free_single_vma(struct madvise_behav= ior *madv_behavior, =20 mmu_notifier_invalidate_range_start(&range); tlb_start_vma(tlb, vma); + walk_ops.walk_lock =3D get_walk_lock(madv_behavior->lock_mode); walk_page_range_vma(vma, range.start, range.end, - &madvise_free_walk_ops, tlb); + &walk_ops, tlb); tlb_end_vma(tlb, vma); mmu_notifier_invalidate_range_end(&range); return 0; @@ -1653,7 +1661,6 @@ static enum madvise_lock_mode get_lock_mode(struct ma= dvise_behavior *madv_behavi case MADV_WILLNEED: case MADV_COLD: case MADV_PAGEOUT: - case MADV_FREE: case MADV_POPULATE_READ: case MADV_POPULATE_WRITE: case MADV_COLLAPSE: @@ -1662,6 +1669,7 @@ static enum madvise_lock_mode get_lock_mode(struct ma= dvise_behavior *madv_behavi return MADVISE_MMAP_READ_LOCK; case MADV_DONTNEED: case MADV_DONTNEED_LOCKED: + case MADV_FREE: return MADVISE_VMA_READ_LOCK; default: return MADVISE_MMAP_WRITE_LOCK; diff --git a/mm/pagewalk.c b/mm/pagewalk.c index e478777c86e1..c984aacc5552 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -420,6 +420,9 @@ static int __walk_page_range(unsigned long start, unsig= ned long end, static inline void process_mm_walk_lock(struct mm_struct *mm, enum page_walk_lock walk_lock) { + if (walk_lock =3D=3D PGWALK_VMA_RDLOCK_VERIFY) + return; + if (walk_lock =3D=3D PGWALK_RDLOCK) mmap_assert_locked(mm); else @@ -437,6 +440,9 @@ static inline void process_vma_walk_lock(struct vm_area= _struct *vma, case PGWALK_WRLOCK_VERIFY: vma_assert_write_locked(vma); break; + case PGWALK_VMA_RDLOCK_VERIFY: + vma_assert_locked(vma); + break; case PGWALK_RDLOCK: /* PGWALK_RDLOCK is handled by process_mm_walk_lock */ break; --=20 2.39.3 (Apple Git-146)