The patch titled
Subject: mm: move FAULT_FLAG_VMA_LOCK check from handle_mm_fault()
has been added to the -mm mm-unstable branch. Its filename is
mm-move-fault_flag_vma_lock-check-from-handle_mm_fault.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-move-fault_flag_vma_lock-check-from-handle_mm_fault.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: mm: move FAULT_FLAG_VMA_LOCK check from handle_mm_fault()
Date: Mon, 24 Jul 2023 19:54:03 +0100
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@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Arjun Roy <arjunroy@xxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Punit Agrawal <punit.agrawal@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 6 ++++++
mm/memory.c | 18 +++++++++---------
2 files changed, 15 insertions(+), 9 deletions(-)
--- a/mm/hugetlb.c~mm-move-fault_flag_vma_lock-check-from-handle_mm_fault
+++ a/mm/hugetlb.c
@@ -6089,6 +6089,12 @@ vm_fault_t hugetlb_fault(struct mm_struc
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
--- a/mm/memory.c~mm-move-fault_flag_vma_lock-check-from-handle_mm_fault
+++ a/mm/memory.c
@@ -5110,10 +5110,10 @@ unlock:
}
/*
- * 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)
@@ -5132,6 +5132,11 @@ static vm_fault_t __handle_mm_fault(stru
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)
@@ -5359,11 +5364,6 @@ vm_fault_t handle_mm_fault(struct vm_are
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.
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
rmap-pass-the-folio-to-__page_check_anon_rmap.patch
highmem-add-memcpy_to_folio-and-memcpy_from_folio.patch
affs-convert-affs_symlink_read_folio-to-use-the-folio.patch
affs-convert-data-read-and-write-to-use-folios.patch
migrate-use-folio_set_bh-instead-of-set_bh_page.patch
ntfs3-convert-ntfs_get_block_vbo-to-use-a-folio.patch
jbd2-use-a-folio-in-jbd2_journal_write_metadata_buffer.patch
buffer-remove-set_bh_page.patch
zswap-make-zswap_store-take-a-folio.patch
memcg-convert-get_obj_cgroup_from_page-to-get_obj_cgroup_from_folio.patch
swap-remove-some-calls-to-compound_head-in-swap_readpage.patch
zswap-make-zswap_load-take-a-folio.patch
mm-remove-config_per_vma_lock-ifdefs.patch
mm-allow-per-vma-locks-on-file-backed-vmas.patch
mm-move-fault_flag_vma_lock-check-from-handle_mm_fault.patch
mm-handle-pud-faults-under-the-vma-lock.patch
mm-handle-some-pmd-faults-under-the-vma-lock.patch
mm-move-fault_flag_vma_lock-check-down-in-handle_pte_fault.patch
mm-move-fault_flag_vma_lock-check-down-from-do_fault.patch
mm-run-the-fault-around-code-under-the-vma-lock.patch
mm-handle-swap-and-numa-pte-faults-under-the-vma-lock.patch
mm-handle-faults-that-merely-update-the-accessed-bit-under-the-vma-lock.patch
