Commit 4ec31152 authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

mm: move FAULT_FLAG_VMA_LOCK check from handle_mm_fault() 

Handle a little more of the page fault path outside the mmap sem.  The
hugetlb path doesn't need to check whether the VMA is anonymous; the
VM_HUGETLB flag is only set on hugetlbfs VMAs.  There should be no
performance change from the previous commit; this is simply a step to ease
bisection of any problems.

Link: https://lkml.kernel.org/r/20230724185410.1124082-4-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarSuren Baghdasaryan <surenb@google.com>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 350f6bbc

mm/hugetlb.c

+6 −0
Original line number Diff line number Diff line
@@ -6062,6 +6062,12 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, 
	int need_wait_lock = 0;

	unsigned long haddr = address & huge_page_mask(h);



	/* TODO: Handle faults under the VMA lock */

	if (flags & FAULT_FLAG_VMA_LOCK) {

		vma_end_read(vma);

		return VM_FAULT_RETRY;

	}



	/*

	 * Serialize hugepage allocation and instantiation, so that we don't

	 * get spurious allocation failures if two CPUs race to instantiate

mm/memory.c

+9 −9
Original line number Diff line number Diff line
@@ -4984,10 +4984,10 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) 
}



/*

 * By the time we get here, we already hold the mm semaphore

 *

 * The mmap_lock may have been released depending on flags and our

 * return value.  See filemap_fault() and __folio_lock_or_retry().

 * On entry, we hold either the VMA lock or the mmap_lock

 * (FAULT_FLAG_VMA_LOCK tells you which).  If VM_FAULT_RETRY is set in

 * the result, the mmap_lock is not held on exit.  See filemap_fault()

 * and __folio_lock_or_retry().

 */

static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,

		unsigned long address, unsigned int flags)
@@ -5006,6 +5006,11 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma, 
	p4d_t *p4d;

	vm_fault_t ret;



	if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) {

		vma_end_read(vma);

		return VM_FAULT_RETRY;

	}



	pgd = pgd_offset(mm, address);

	p4d = p4d_alloc(mm, pgd, address);

	if (!p4d)
@@ -5222,11 +5227,6 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address, 
		goto out;

	}



	if ((flags & FAULT_FLAG_VMA_LOCK) && !vma_is_anonymous(vma)) {

		vma_end_read(vma);

		return VM_FAULT_RETRY;

	}



	/*

	 * Enable the memcg OOM handling for faults triggered in user

	 * space.  Kernel faults are handled more gracefully.