linux-kernel - Re: [PATCH v2 6/9] hugetlb: add vma based lock for pmd sharing

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Date:   Thu, 15 Sep 2022 13:25:06 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Muchun Song <songmuchun@...edance.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Prakash Sangappa <prakash.sangappa@...cle.com>,
        James Houghton <jthoughton@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Ray Fucillo <Ray.Fucillo@...ersystems.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 6/9] hugetlb: add vma based lock for pmd sharing

On 09/14/22 15:18, Mike Kravetz wrote:
> Allocate a new hugetlb_vma_lock structure and hang off vm_private_data
> for synchronization use by vmas that could be involved in pmd sharing.
> This data structure contains a rw semaphore that is the primary tool
> used for synchronization.
> 
> This new structure is ref counted, so that it can exist when NOT attached
> to a vma.  This is only helpful in resolving lock ordering issues where
> code may need to obtain the vma_lock while there are no guarantees the
> vma may go away.  By obtaining a ref on the structure, it can be
> guaranteed that at least the rw semaphore will not go away.
> 
> Only add infrastructure for the new lock here.  Actual use will be added
> in subsequent patches.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
> ---
>  include/linux/hugetlb.h |  43 ++++++++-
>  kernel/fork.c           |   6 +-
>  mm/hugetlb.c            | 202 ++++++++++++++++++++++++++++++++++++----
>  mm/rmap.c               |   8 +-
>  4 files changed, 235 insertions(+), 24 deletions(-)

Reviewers - FYI, the following was added to address a build issue caused
by this patch.

>From 8b3031350154e8e401ccfbc5e71cb95ef654d017 Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@...cle.com>
Date: Thu, 15 Sep 2022 09:33:44 -0700
Subject: [PATCH] hugetlb: fix build issue for missing hugetlb_vma_lock_release

Add a stub for hugetlb_vma_lock_release to build in the case
CONFIG_HUGETLB_PAGE && !CONFIG_ARCH_WANT_HUGE_PMD_SHARE.

Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 mm/hugetlb.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2207300791e5..cc7877da18d7 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -7008,6 +7008,10 @@ void hugetlb_vma_assert_locked(struct vm_area_struct *vma)
 {
 }
 
+void hugetlb_vma_lock_release(struct kref *kref)
+{
+}
+
 static void hugetlb_vma_lock_free(struct vm_area_struct *vma)
 {
 }
-- 
2.37.2