linux-kernel - [RFC PATCH v2 23/47] rmap: update hugetlb lock comment for HGM

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Message-ID: <20221021163703.3218176-24-jthoughton@google.com>
Date:   Fri, 21 Oct 2022 16:36:39 +0000
From:   James Houghton <jthoughton@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Peter Xu <peterx@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Mina Almasry <almasrymina@...gle.com>,
        "Zach O'Keefe" <zokeefe@...gle.com>,
        Manish Mishra <manish.mishra@...anix.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        James Houghton <jthoughton@...gle.com>
Subject: [RFC PATCH v2 23/47] rmap: update hugetlb lock comment for HGM

The VMA lock is used to prevent high-granularity HugeTLB mappings from
being collapsed while other threads are doing high-granularity page
table walks.

Signed-off-by: James Houghton <jthoughton@...gle.com>
---
 mm/rmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 19850d955aea..527463c1e936 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -47,7 +47,8 @@
  *
  * hugetlbfs PageHuge() take locks in this order:
  *   hugetlb_fault_mutex (hugetlbfs specific page fault mutex)
- *     vma_lock (hugetlb specific lock for pmd_sharing)
+ *     vma_lock (hugetlb specific lock for pmd_sharing and high-granularity
+ *               mapping)
  *       mapping->i_mmap_rwsem (also used for hugetlb pmd sharing)
  *         page->flags PG_locked (lock_page)
  */
-- 
2.38.0.135.g90850a2211-goog