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Wed, 28 Jun 2023 10:25:43 -0700 (PDT) Date: Wed, 28 Jun 2023 10:25:28 -0700 In-Reply-To: <20230628172529.744839-1-surenb@google.com> Mime-Version: 1.0 References: <20230628172529.744839-1-surenb@google.com> X-Mailer: git-send-email 2.41.0.162.gfafddb0af9-goog Message-ID: <20230628172529.744839-6-surenb@google.com> Subject: [PATCH v5 5/6] mm: handle swap page faults under per-VMA lock From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: willy@infradead.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com, peterx@redhat.com, ying.huang@intel.com, david@redhat.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, pasha.tatashin@soleen.com, surenb@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com X-Rspamd-Queue-Id: F1FF12001E X-Rspam-User: X-Stat-Signature: b4m1cz74aq5gg4jo98xxxbbuz4m63e6j X-Rspamd-Server: rspam03 X-HE-Tag: 1687973144-575250 X-HE-Meta: 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 E3/to+Mt 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. Signed-off-by: Suren Baghdasaryan Acked-by: Peter Xu Tested-by: Alistair Popple Reviewed-by: Alistair Popple --- 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 fec149585985..bbaec479bf98 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -723,6 +723,14 @@ static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached) struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address); +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); +} + #else /* CONFIG_PER_VMA_LOCK */ static inline void vma_init_lock(struct vm_area_struct *vma) {} @@ -736,6 +744,11 @@ static inline void vma_assert_write_locked(struct vm_area_struct *vma) {} static inline void vma_mark_detached(struct vm_area_struct *vma, bool detached) {} +static inline void release_fault_lock(struct vm_fault *vmf) +{ + mmap_read_unlock(vmf->vma->vm_mm); +} + #endif /* CONFIG_PER_VMA_LOCK */ /* diff --git a/mm/filemap.c b/mm/filemap.c index 52bcf12dcdbf..d4d8f474e0c5 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1703,27 +1703,26 @@ static int __folio_lock_async(struct folio *folio, struct wait_page_queue *wait) * Return values: * 0 - folio is locked. * VM_FAULT_RETRY - 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 @@ -1735,7 +1734,7 @@ 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 345080052003..4fb8ecfc6d13 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3712,12 +3712,6 @@ 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)) { @@ -3727,6 +3721,16 @@ 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);