linux-kernel - Re: [PATCH v7 2/4] mm/memory.c: Update local TLB if PTE entry exists

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Message-ID: <b577bca0-4218-12e6-d63f-0d12cb0a60f9@loongson.cn>
Date:   Fri, 29 May 2020 08:59:31 +0800
From:   maobibo <maobibo@...ngson.cn>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhc@...ote.com>,
        Paul Burton <paulburton@...nel.org>,
        Dmitry Korotin <dkorotin@...ecomp.com>,
        Philippe Mathieu-Daudé <f4bug@...at.org>,
        Stafford Horne <shorne@...il.com>,
        Steven Price <steven.price@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "Maciej W. Rozycki" <macro@....com>, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH v7 2/4] mm/memory.c: Update local TLB if PTE entry exists



On 05/29/2020 03:23 AM, Andrew Morton wrote:
> On Wed, 27 May 2020 10:25:18 +0800 Bibo Mao <maobibo@...ngson.cn> wrote:
> 
>> If two threads concurrently fault at the same page, the thread that
>> won the race updates the PTE and its local TLB. For now, the other
>> thread gives up, simply does nothing, and continues.
>>
>> It could happen that this second thread triggers another fault, whereby
>> it only updates its local TLB while handling the fault. Instead of
>> triggering another fault, let's directly update the local TLB of the
>> second thread. Function update_mmu_tlb is used here to update local
>> TLB on the second thread, and it is defined as empty on other arches.
>>
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2752,6 +2752,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
>>  		new_page = old_page;
>>  		page_copied = 1;
>>  	} else {
>> +		update_mmu_tlb(vma, vmf->address, vmf->pte);
>>  		mem_cgroup_cancel_charge(new_page, memcg, false);
>>  	}
>>  
> 
> When applying your patches on top of the -mm tree's changes, the above
> hunk didn't apply.  The entire `else' block was removed by
> https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-convert-anon-and-file-thp-to-new-mem_cgroup_charge-api.patch
> 
> I assumed that dropping this hunk was appropriate.  Please check?
yes, that is appropriate. Sorry to bother you, originally I should format the
patch based on mm-tree.