linux-kernel - [PATCH v2 0/5] Handle hugetlb faults under the VMA lock

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Date: Wed, 21 Feb 2024 15:47:27 -0800
From: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org,
	muchun.song@...ux.dev,
	willy@...radead.org,
	"Vishal Moola (Oracle)" <vishal.moola@...il.com>
Subject: [PATCH v2 0/5] Handle hugetlb faults under the VMA lock

It is generally safe to handle hugetlb faults under the VMA lock. The
only time this is unsafe is when no anon_vma has been allocated to this
vma yet, so we can use vmf_anon_prepare() instead of anon_vma_prepare()
to bailout if necessary. This should only happen for the first hugetlb
page in the vma.

Additionally, this patchset begins to use struct vm_fault within
hugetlb_fault(). This works towards cleaning up hugetlb code, and should
significantly reduce the number of arguments passed to functions.

-----
The last patch in this series may cause ltp hugemmap10 to "fail". This
is because vmf_anon_prepare() may bailout with no anon_vma under the VMA
lock after allocating a folio for the hugepage. In free_huge_folio(),
this folio is completely freed on bailout iff there is a surplus of
hugetlb pages. This will remove a folio off the freelist and decrement
the number of hugepages while ltp expects these counters to remain
unchanged on failure. The rest of the ltp testcases pass.

v2:
  - Removed unnecessary variables and indentations
  - Declare struct vm_fault in hugetlb_fault and pass it down as an
  argument instead of defining it in each called function.
  - Moved vmf_anon_prepare() declaration to mm/internal.h from
  include/linux/hugetlb.h


Vishal Moola (Oracle) (5):
  mm/memory: Change vmf_anon_prepare() to be non-static
  hugetlb: Move vm_struct declaration to the top of hugetlb_fault()
  hugetlb: Pass struct vm_fault through to hugetlb_handle_userfault()
  hugetlb: Use vmf_anon_prepare() instead of anon_vma_prepare()
  hugetlb: Allow faults to be handled under the VMA lock

 mm/hugetlb.c  | 88 ++++++++++++++++++++-------------------------------
 mm/internal.h |  1 +
 mm/memory.c   |  2 +-
 3 files changed, 36 insertions(+), 55 deletions(-)

-- 
2.43.0