linux-kernel - Re: [PATCH v4 10/15] riscv: pgtable: move pagetable_dtor() to __tlb_remove

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Message-ID: <ee393a7f-d01e-4e5d-9bf8-779795613af1@arm.com>
Date: Tue, 7 Jan 2025 10:57:59 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Qi Zheng <zhengqi.arch@...edance.com>
Cc: agordeev@...ux.ibm.com, palmer@...belt.com, tglx@...utronix.de,
 david@...hat.com, jannh@...gle.com, hughd@...gle.com, yuzhao@...gle.com,
 willy@...radead.org, muchun.song@...ux.dev, vbabka@...nel.org,
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 arnd@...db.de, will@...nel.org, aneesh.kumar@...nel.org, npiggin@...il.com,
 dave.hansen@...ux.intel.com, rppt@...nel.org, ryan.roberts@....com,
 linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
 linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
 linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
 linux-kernel@...r.kernel.org, x86@...nel.org, linux-arch@...r.kernel.org,
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 linux-sh@...r.kernel.org, linux-um@...ts.infradead.org,
 peterz@...radead.org, akpm@...ux-foundation.org
Subject: Re: [PATCH v4 10/15] riscv: pgtable: move pagetable_dtor() to
 __tlb_remove_table()

On 06/01/2025 04:49, Qi Zheng wrote:
> [...]
>
>> Once this is done, we should be able to replace all those confusing
>> calls to tlb_remove_page() on PTPs with tlb_remove_table() and remove
>> the explicit call to pagetable_dtor(). AIUI this is essentially what
>> Peter suggested on v3 [2].
>
> Since this patch series is mainly for bug fix, I think that these things
> can be done in separate patch series later.

Sure that's fair.

>
>>
>> [...]
>>
>>> Or can we just not let tlb_remove_table() fall back to
>>> tlb_remove_page()? Like the following:
>>>
>>> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
>>> index a59205863f431..354ffaa4bd120 100644
>>> --- a/include/asm-generic/tlb.h
>>> +++ b/include/asm-generic/tlb.h
>>> @@ -195,8 +195,6 @@
>>>    *  various ptep_get_and_clear() functions.
>>>    */
>>>
>>> -#ifdef CONFIG_MMU_GATHER_TABLE_FREE
>>> -
>>>   struct mmu_table_batch {
>>>   #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE
>>>          struct rcu_head         rcu;
>>> @@ -219,16 +217,6 @@ static inline void __tlb_remove_table(void *table)
>>>
>>>   extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
>>>
>>> -#else /* !CONFIG_MMU_GATHER_HAVE_TABLE_FREE */
>>> -
>>> -/*
>>> - * Without MMU_GATHER_TABLE_FREE the architecture is assumed to have
>>> page based
>>> - * page directories and we can use the normal page batching to free
>>> them.
>>> - */
>>> -#define tlb_remove_table(tlb, page) tlb_remove_page((tlb), (page))
>>
>> We still need a different implementation of tlb_remove_table() in this
>> case. We could define it inline here:
>>
>> static inline void tlb_remove_table(struct mmu_gather *tlb, void *table)
>> {
>>      struct page *page = table;
>>
>>      pagetable_dtor(page_ptdesc(page));
>>      tlb_remove_page(page);
>> }
>
> Right. As I said above, will add this to the updated patch #8.

I think it would be preferable to make it a standalone patch, because
this is a change to generic code that could in principle impact other
arch's too.

- Kevin