Commit f4981502 authored by Liu Shixin's avatar Liu Shixin Committed by Andrew Morton
Browse files

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: default avatarLiu Shixin <liushixin2@huawei.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 13cc3784

Documentation/admin-guide/mm/transhuge.rst

+3 −4
Original line number Diff line number Diff line
@@ -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

mm/huge_memory.c

+1 −1
Original line number Diff line number Diff line
@@ -163,7 +163,6 @@ static bool get_huge_zero_page(void) 
		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 @@ static bool get_huge_zero_page(void) 
	/* 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;

}