linux-kernel - Re: [RFC PATCH v2 2/3] mm: Add PUD level pagetable account

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Date:   Thu, 23 Jun 2022 11:32:37 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     akpm@...ux-foundation.org, willy@...radead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 2/3] mm: Add PUD level pagetable account



On 6/22/2022 10:38 PM, Mike Rapoport wrote:
> On Wed, Jun 22, 2022 at 04:58:53PM +0800, Baolin Wang wrote:
>> Now the PUD level ptes are always protected by mm->page_table_lock,
>> which means no split pagetable lock needed. So the generic PUD level
>> pagetable pages allocation will not call pgtable_pte_page_ctor/dtor(),
>> that means we will miss to account PUD level pagetable pages.
>>
>> Adding pagetable account by calling pgtable_set_and_inc() or
>> pgtable_clear_and_dec() when allocating or freeing PUD level pagetable
>> pages to help to get an accurate pagetable accounting.
>>
>> Moreover this patch will also mark the PUD level pagetable with PG_table
>> flag, which will help to do sanity validation in unpoison_memory() and
>> get more accurate pagetable accounting by /proc/kpageflags interface.
>>
>> Meanwhile converting the architectures with using generic PUD pagatable
>> allocation to add corresponding pgtable_set_and_inc() or pgtable_clear_and_dec()
>> to account PUD level pagetable.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> ---
>>   arch/arm64/include/asm/tlb.h         |  5 ++++-
>>   arch/loongarch/include/asm/pgalloc.h | 11 ++++++++---
>>   arch/mips/include/asm/pgalloc.h      | 11 ++++++++---
>>   arch/s390/include/asm/tlb.h          |  1 +
>>   arch/x86/mm/pgtable.c                |  5 ++++-
>>   include/asm-generic/pgalloc.h        | 12 ++++++++++--
>>   6 files changed, 35 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
>> index c995d1f..47e0623 100644
>> --- a/arch/arm64/include/asm/tlb.h
>> +++ b/arch/arm64/include/asm/tlb.h
>> @@ -94,7 +94,10 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
>>   static inline void __pud_free_tlb(struct mmu_gather *tlb, pud_t *pudp,
>>   				  unsigned long addr)
>>   {
>> -	tlb_remove_table(tlb, virt_to_page(pudp));
>> +	struct page *page = virt_to_page(pudp);
>> +
>> +	pgtable_clear_and_dec(page);
>> +	tlb_remove_table(tlb, page);
>>   }
>>   #endif
>>   
>> diff --git a/arch/loongarch/include/asm/pgalloc.h b/arch/loongarch/include/asm/pgalloc.h
>> index b0a57b2..50a896f 100644
>> --- a/arch/loongarch/include/asm/pgalloc.h
>> +++ b/arch/loongarch/include/asm/pgalloc.h
>> @@ -89,10 +89,15 @@ static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address)
>>   static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long address)
>>   {
>>   	pud_t *pud;
>> +	struct page *pg;
> 
> 	struct page *page;
> 
> looks better IMO.

Sure.

> 
>> +
>> +	pg = alloc_pages(GFP_KERNEL & ~__GFP_HIGHMEM, PUD_ORDER);
>> +	if (!pg)
>> +		return NULL;
>>   
>> -	pud = (pud_t *) __get_free_pages(GFP_KERNEL, PUD_ORDER);
>> -	if (pud)
>> -		pud_init((unsigned long)pud, (unsigned long)invalid_pmd_table);
>> +	pgtable_set_and_inc(pg);
>> +	pud = (pud_t *)page_address(pg);
> 
> I don't think __get_free_pages() should be replaced with alloc_pages()
> here, just call pgtable_set_and_inc() with virt_to_page(pud).
> 
> The same applies for the cases below.

Sure. Will do in next version. Thanks.