From 1235ccd05b6dd6970ff50baea99aa994023fbc4a Mon Sep 17 00:00:00 2001 From: Suren Baghdasaryan Date: Fri, 30 Jun 2023 14:19:56 -0700 Subject: mm: handle swap page faults under per-VMA lock When page fault is handled under per-VMA lock protection, all swap page faults are retried with mmap_lock because folio_lock_or_retry has to drop and reacquire mmap_lock if folio could not be immediately locked. Follow the same pattern as mmap_lock to drop per-VMA lock when waiting for folio and retrying once folio is available. With this obstacle removed, enable do_swap_page to operate under per-VMA lock protection. Drivers implementing ops->migrate_to_ram might still rely on mmap_lock, therefore we have to fall back to mmap_lock in that particular case. Note that the only time do_swap_page calls synchronous swap_readpage is when SWP_SYNCHRONOUS_IO is set, which is only set for QUEUE_FLAG_SYNCHRONOUS devices: brd, zram and nvdimms (both btt and pmem). Therefore we don't sleep in this path, and there's no need to drop the mmap or per-VMA lock. Link: https://lkml.kernel.org/r/20230630211957.1341547-6-surenb@google.com Signed-off-by: Suren Baghdasaryan Tested-by: Alistair Popple Reviewed-by: Alistair Popple Acked-by: Peter Xu Cc: Al Viro Cc: Christian Brauner Cc: Christoph Hellwig Cc: David Hildenbrand Cc: David Howells Cc: Davidlohr Bueso Cc: Hillf Danton Cc: "Huang, Ying" Cc: Hugh Dickins Cc: Jan Kara Cc: Johannes Weiner Cc: Josef Bacik Cc: Laurent Dufour Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcox Cc: Michal Hocko Cc: Michel Lespinasse Cc: Minchan Kim Cc: Pavel Tatashin Cc: Punit Agrawal Cc: Vlastimil Babka Cc: Yu Zhao Signed-off-by: Andrew Morton --- include/linux/mm.h | 13 +++++++++++++ mm/filemap.c | 17 ++++++++--------- mm/memory.c | 16 ++++++++++------ 3 files changed, 31 insertions(+), 15 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 939386e0aeda..0d16208178c7 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -729,6 +729,14 @@ static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached) vma->detached = detached; } +static inline void release_fault_lock(struct vm_fault *vmf) +{ + if (vmf->flags & FAULT_FLAG_VMA_LOCK) + vma_end_read(vmf->vma); + else + mmap_read_unlock(vmf->vma->vm_mm); +} + struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address); @@ -749,6 +757,11 @@ static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, return NULL; } +static inline void release_fault_lock(struct vm_fault *vmf) +{ + mmap_read_unlock(vmf->vma->vm_mm); +} + #endif /* CONFIG_PER_VMA_LOCK */ extern const struct vm_operations_struct vma_dummy_vm_ops; diff --git a/mm/filemap.c b/mm/filemap.c index 40514493014a..8040545954bc 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1671,27 +1671,26 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait) * Return values: * 0 - folio is locked. * non-zero - folio is not locked. - * mmap_lock has been released (mmap_read_unlock(), unless flags had both - * FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in - * which case mmap_lock is still held. + * mmap_lock or per-VMA lock has been released (mmap_read_unlock() or + * vma_end_read()), unless flags had both FAULT_FLAG_ALLOW_RETRY and + * FAULT_FLAG_RETRY_NOWAIT set, in which case the lock is still held. * * If neither ALLOW_RETRY nor KILLABLE are set, will always return 0 - * with the folio locked and the mmap_lock unperturbed. + * with the folio locked and the mmap_lock/per-VMA lock is left unperturbed. */ vm_fault_t __folio_lock_or_retry(struct folio *folio, struct vm_fault *vmf) { - struct mm_struct *mm = vmf->vma->vm_mm; unsigned int flags = vmf->flags; if (fault_flag_allow_retry_first(flags)) { /* - * CAUTION! In this case, mmap_lock is not released - * even though return VM_FAULT_RETRY. + * CAUTION! In this case, mmap_lock/per-VMA lock is not + * released even though returning VM_FAULT_RETRY. */ if (flags & FAULT_FLAG_RETRY_NOWAIT) return VM_FAULT_RETRY; - mmap_read_unlock(mm); + release_fault_lock(vmf); if (flags & FAULT_FLAG_KILLABLE) folio_wait_locked_killable(folio); else @@ -1703,7 +1702,7 @@ vm_fault_t __folio_lock_or_retry(struct folio *folio, struct vm_fault *vmf) ret = __folio_lock_killable(folio); if (ret) { - mmap_read_unlock(mm); + release_fault_lock(vmf); return VM_FAULT_RETRY; } } else { diff --git a/mm/memory.c b/mm/memory.c index 080e1d59d752..5748a41c164c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3746,12 +3746,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) if (!pte_unmap_same(vmf)) goto out; - if (vmf->flags & FAULT_FLAG_VMA_LOCK) { - ret = VM_FAULT_RETRY; - vma_end_read(vma); - goto out; - } - entry = pte_to_swp_entry(vmf->orig_pte); if (unlikely(non_swap_entry(entry))) { if (is_migration_entry(entry)) { @@ -3761,6 +3755,16 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) vmf->page = pfn_swap_entry_to_page(entry); ret = remove_device_exclusive_entry(vmf); } else if (is_device_private_entry(entry)) { + if (vmf->flags & FAULT_FLAG_VMA_LOCK) { + /* + * migrate_to_ram is not yet ready to operate + * under VMA lock. + */ + vma_end_read(vma); + ret = VM_FAULT_RETRY; + goto out; + } + vmf->page = pfn_swap_entry_to_page(entry); vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); -- cgit