Commit 063e60d8 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

mm: handle faults that merely update the accessed bit under the VMA lock 

Move FAULT_FLAG_VMA_LOCK check out of handle_pte_fault().  This should
have a significant performance improvement for mmaped files.  Write faults
(on read-only shared pages) still take the mmap lock as we do not want to
audit all the implementations of ->pfn_mkwrite() and ->page_mkwrite(). 
However write-faults on private mappings are handled under the VMA lock.

[willy@infradead.org: address "suspicious RCU usage" warning]
  Link: https://lkml.kernel.org/r/ZMK7jwpI4uD6tKrF@casper.infradead.org
Link: https://lkml.kernel.org/r/20230724185410.1124082-11-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4c2f803a

mm/memory.c

+17 −6
Original line number Diff line number Diff line
@@ -3268,6 +3268,11 @@ static vm_fault_t wp_pfn_shared(struct vm_fault *vmf) 
		vm_fault_t ret;



		pte_unmap_unlock(vmf->pte, vmf->ptl);

		if (vmf->flags & FAULT_FLAG_VMA_LOCK) {

			vma_end_read(vmf->vma);

			return VM_FAULT_RETRY;

		}



		vmf->flags |= FAULT_FLAG_MKWRITE;

		ret = vma->vm_ops->pfn_mkwrite(vmf);

		if (ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE))
@@ -3290,6 +3295,12 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf, struct folio *folio) 
		vm_fault_t tmp;



		pte_unmap_unlock(vmf->pte, vmf->ptl);

		if (vmf->flags & FAULT_FLAG_VMA_LOCK) {

			folio_put(folio);

			vma_end_read(vmf->vma);

			return VM_FAULT_RETRY;

		}



		tmp = do_page_mkwrite(vmf, folio);

		if (unlikely(!tmp || (tmp &

				      (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))) {
@@ -3431,6 +3442,12 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) 
		return 0;

	}

copy:

	if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma->anon_vma) {

		pte_unmap_unlock(vmf->pte, vmf->ptl);

		vma_end_read(vmf->vma);

		return VM_FAULT_RETRY;

	}



	/*

	 * Ok, we need to copy. Oh, well..

	 */
@@ -4985,12 +5002,6 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) 
	if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))

		return do_numa_page(vmf);



	if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vmf->vma)) {

		pte_unmap(vmf->pte);

		vma_end_read(vmf->vma);

		return VM_FAULT_RETRY;

	}



	spin_lock(vmf->ptl);

	entry = vmf->orig_pte;

	if (unlikely(!pte_same(ptep_get(vmf->pte), entry))) {