linux-kernel - Re: [PATCH 2/4] mm: mremap: use flush_pmd_tlb_range() in move_normal

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Message-ID: <91863dc8-1f70-ba29-b36d-9261dd594574@huawei.com>
Date:   Mon, 31 Jul 2023 19:20:03 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Mina Almasry <almasrymina@...gle.com>, <kirill@...temov.name>,
        <joel@...lfernandes.org>, <william.kucharski@...cle.com>,
        <kaleshsingh@...gle.com>, <linux-mm@...ck.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] mm: mremap: use flush_pmd_tlb_range() in
 move_normal_pmd()



On 2023/7/31 19:05, Catalin Marinas wrote:
> On Mon, Jul 31, 2023 at 03:48:27PM +0800, Kefeng Wang wrote:
>> Archs may need to do special things when flushing thp tlb,
>> so use the more applicable flush_pud_tlb_range() instead of
>> flush_tlb_range().
>>
>> Fixes: 2c91bd4a4e2e ("mm: speed up mremap by 20x on large regions")
>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
>> ---
>>   mm/mremap.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/mremap.c b/mm/mremap.c
>> index 11e06e4ab33b..1883205fa22b 100644
>> --- a/mm/mremap.c
>> +++ b/mm/mremap.c
>> @@ -284,7 +284,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
>>   	VM_BUG_ON(!pmd_none(*new_pmd));
>>   
>>   	pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
>> -	flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
>> +	flush_pmd_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
> 
> I don't think that's correct for arm64. The assumption in the
> flush_p*d_tlb_range() was that they are called only for block mappings
> at that p*d level (and we use FEAT_TTL on arm64 indicating that the leaf
> level is level 2 for pmd, 1 for pud). IIUC move_normal_pmd() is only
> called for table pmds which would have a leaf level of 3 (the pte).

oops, yes, this is for NORMAL_PMD case, not HPAGE_PMD, please ignore 
patch 2/3.

> 
> Same for the next patch doing the equivalent for the pud.
>