From f4981502088f8ea704beeedf3470e1d53bc2e46c Mon Sep 17 00:00:00 2001 From: Liu Shixin Date: Fri, 9 Sep 2022 10:16:53 +0800 Subject: mm/huge_memory: prevent THP_ZERO_PAGE_ALLOC increased twice A user who reads THP_ZERO_PAGE_ALLOC may be more concerned about the huge zero pages that are really allocated for thp. It is misleading to increase THP_ZERO_PAGE_ALLOC twice if two threads call get_huge_zero_page concurrently. Don't increase the value if the huge page is not really used. Update Documentation/admin-guide/mm/transhuge.rst to suit. Link: https://lkml.kernel.org/r/20220909021653.3371879-1-liushixin2@huawei.com Signed-off-by: Liu Shixin Cc: Alexander Potapenko Cc: Vlastimil Babka Cc: Andrea Arcangeli Cc: Kefeng Wang Cc: "Kirill A. Shutemov" Cc: Mike Kravetz Signed-off-by: Andrew Morton --- Documentation/admin-guide/mm/transhuge.rst | 7 +++---- mm/huge_memory.c | 2 +- 2 files changed, 4 insertions(+), 5 deletions(-) diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst index c9c37f16eef8..8e3418ec4503 100644 --- a/Documentation/admin-guide/mm/transhuge.rst +++ b/Documentation/admin-guide/mm/transhuge.rst @@ -366,10 +366,9 @@ thp_split_pmd page table entry. thp_zero_page_alloc - is incremented every time a huge zero page is - successfully allocated. It includes allocations which where - dropped due race with other allocation. Note, it doesn't count - every map of the huge zero page, only its allocation. + is incremented every time a huge zero page used for thp is + successfully allocated. Note, it doesn't count every map of + the huge zero page, only its allocation. thp_zero_page_alloc_failed is incremented if kernel fails to allocate diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 36ef79b85195..4938defe4e73 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -163,7 +163,6 @@ retry: count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED); return false; } - count_vm_event(THP_ZERO_PAGE_ALLOC); preempt_disable(); if (cmpxchg(&huge_zero_page, NULL, zero_page)) { preempt_enable(); @@ -175,6 +174,7 @@ retry: /* We take additional reference here. It will be put back by shrinker */ atomic_set(&huge_zero_refcount, 2); preempt_enable(); + count_vm_event(THP_ZERO_PAGE_ALLOC); return true; } -- cgit v1.2.3