Re: [linus:master] [migrate_pages] 7e12beb8ca: vm-scalability.throughput -3.4% regression

["Huang, Ying" <ying.huang@intel.com>]

Hi, Yujie,

kernel test robot <yujie.liu@intel.com> writes:

> Hello,
>
> FYI, we noticed a -3.4% regression of vm-scalability.throughput due to commit:
>
> commit: 7e12beb8ca2ac98b2ec42e0ea4b76cdc93b58654 ("migrate_pages: batch flushing TLB")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
> in testcase: vm-scalability
> on test machine: 96 threads 2 sockets Intel(R) Xeon(R) Platinum 8260L CPU @ 2.40GHz (Cascade Lake) with 128G memory
> with following parameters:
>
> 	runtime: 300s
> 	size: 512G
> 	test: anon-cow-rand-mt
> 	cpufreq_governor: performance
>
> test-description: The motivation behind this suite is to exercise functions and regions of the mm/ of the Linux kernel which are of interest to us.
> test-url: https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git/
>
>
> If you fix the issue, kindly add following tag
> | Reported-by: kernel test robot <yujie.liu@intel.com>
> | Link: https://lore.kernel.org/oe-lkp/202303192325.ecbaf968-yujie.liu@intel.com
>

Thanks a lot for report!  Can you try whether the debug patch as
below can restore the regression?

Best Regards,
Huang, Ying

-------------------------------------8<------------------------------------
From 1ac61967b54bbdc1ca20af16f9dfb2507a4d4811 Mon Sep 17 00:00:00 2001
From: Huang Ying <ying.huang@intel.com>
Date: Mon, 20 Mar 2023 15:48:39 +0800
Subject: [PATCH] dbg, rmap: avoid flushing TLB in batch if PTE is inaccessible

Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 mm/rmap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 8632e02661ac..3c7c43642d7c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1582,7 +1582,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 				 */
 				pteval = ptep_get_and_clear(mm, address, pvmw.pte);
 
-				set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
+				if (pte_accessible(mm, pteval))
+					set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
 			} else {
 				pteval = ptep_clear_flush(vma, address, pvmw.pte);
 			}
@@ -1963,7 +1964,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 				 */
 				pteval = ptep_get_and_clear(mm, address, pvmw.pte);
 
-				set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
+				if (pte_accessible(mm, pteval))
+					set_tlb_ubc_flush_pending(mm, pte_dirty(pteval));
 			} else {
 				pteval = ptep_clear_flush(vma, address, pvmw.pte);
 			}
-- 
2.30.2