linux-kernel - Re: [linus:master] [mm] c0bff412e6: stress-ng.clone.ops_per

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Message-ID: <439265d8-e71e-41db-8a46-55366fdd334e@intel.com>
Date: Thu, 1 Aug 2024 14:39:12 +0800
From: "Yin, Fengwei" <fengwei.yin@...el.com>
To: David Hildenbrand <david@...hat.com>, kernel test robot
	<oliver.sang@...el.com>, Peter Xu <peterx@...hat.com>
CC: <oe-lkp@...ts.linux.dev>, <lkp@...el.com>, <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, Huacai Chen
	<chenhuacai@...nel.org>, Jason Gunthorpe <jgg@...dia.com>, Matthew Wilcox
	<willy@...radead.org>, Nathan Chancellor <nathan@...nel.org>, Ryan Roberts
	<ryan.roberts@....com>, WANG Xuerui <kernel@...0n.name>,
	<linux-mm@...ck.org>, <ying.huang@...el.com>, <feng.tang@...el.com>
Subject: Re: [linus:master] [mm] c0bff412e6: stress-ng.clone.ops_per_sec -2.9%
 regression

Hi David,

On 7/30/2024 4:11 PM, David Hildenbrand wrote:
> On 30.07.24 07:00, kernel test robot wrote:
>>
>>
>> Hello,
>>
>> kernel test robot noticed a -2.9% regression of 
>> stress-ng.clone.ops_per_sec on:
> 
> Is that test even using hugetlb? Anyhow, this pretty much sounds like 
> noise and can be ignored.
> 
It's not about hugetlb. It looks like related with the change:

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 888353c209c03..7577fe7debafc 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -1095,7 +1095,12 @@ PAGEFLAG(Isolated, isolated, PF_ANY);
  static __always_inline int PageAnonExclusive(const struct page *page)
  {
         VM_BUG_ON_PGFLAGS(!PageAnon(page), page);
-       VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page);
+       /*
+        * HugeTLB stores this information on the head page; THP keeps 
it per
+        * page
+        */
+       if (PageHuge(page))
+               page = compound_head(page);
         return test_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags);


The PageAnonExclusive() function is changed. And the profiling data
showed it:

       0.00            +3.9        3.90 
perf-profile.calltrace.cycles-pp.folio_try_dup_anon_rmap_ptes.copy_present_ptes.copy_pte_range.copy_p4d_range.copy_page_range

According 
https://download.01.org/0day-ci/archive/20240730/202407301049.5051dc19-oliver.sang@intel.com/config-6.9.0-rc4-00197-gc0bff412e67b:
	# CONFIG_DEBUG_VM is not set
So maybe such code change could bring difference?

And yes. 2.9% regression can be in noise range. Thanks.


Regards
Yin, Fengwei