linux-kernel - Re: [PATCH v3 1/2] mm: use update_mmu

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Date:   Fri, 30 Sep 2022 15:31:35 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Qi Zheng <zhengqi.arch@...edance.com>, maobibo@...ngson.cn,
        chenhuacai@...ngson.cn, songmuchun@...edance.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        loongarch@...ts.linux.dev, chris@...kel.net, jcmvbkbc@...il.com
Subject: Re: [PATCH v3 1/2] mm: use update_mmu_tlb() on the second thread

On Fri, 30 Sep 2022 10:44:21 +0200 David Hildenbrand <david@...hat.com> wrote:

> > Oh, this is better. Hi Andrew, do I need to resend the v4?
> > 
> 
> I assume he can squash it, most probably no need to resend. :)


From: Qi Zheng <zhengqi.arch@...edance.com>
Subject: mm: use update_mmu_tlb() on the second thread
Date: Thu, 29 Sep 2022 19:23:17 +0800

As message in commit 7df676974359 ("mm/memory.c: Update local TLB if PTE
entry exists") said, we should update local TLB only on the second thread.
So in the do_anonymous_page() here, we should use update_mmu_tlb()
instead of update_mmu_cache() on the second thread.

As David pointed out, this is a performance improvement, not a
correctness fix.

Link: https://lkml.kernel.org/r/20220929112318.32393-2-zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
Reviewed-by: Muchun Song <songmuchun@...edance.com>
Acked-by: David Hildenbrand <david@...hat.com>
Cc: Bibo Mao <maobibo@...ngson.cn>
Cc: Chris Zankel <chris@...kel.net>
Cc: Huacai Chen <chenhuacai@...ngson.cn>
Cc: Max Filippov <jcmvbkbc@...il.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 mm/memory.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memory.c~mm-use-update_mmu_tlb-on-the-second-thread
+++ a/mm/memory.c
@@ -4136,7 +4136,7 @@ static vm_fault_t do_anonymous_page(stru
 	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
 			&vmf->ptl);
 	if (!pte_none(*vmf->pte)) {
-		update_mmu_cache(vma, vmf->address, vmf->pte);
+		update_mmu_tlb(vma, vmf->address, vmf->pte);
 		goto release;
 	}
 
_