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

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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: Matthew 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-07-24 19:54:10 +01:00 • committed by Andrew Morton
parent 4c2f803abb
commit 063e60d806
1 changed files with 17 additions and 6 deletions
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23
mm/memory.c
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@ -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 @@ reuse:
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))) {