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Fri, 03 Jan 2025 01:35:45 -0800 (PST) Message-ID: <31e1a033-00a7-4953-81e7-0caedd0227a9@bytedance.com> Date: Fri, 3 Jan 2025 17:35:30 +0800 Precedence: bulk X-Mailing-List: linux-m68k@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 10/15] riscv: pgtable: move pagetable_dtor() to __tlb_remove_table() Content-Language: en-US From: Qi Zheng To: Kevin Brodsky , peterz@infradead.org Cc: agordeev@linux.ibm.com, palmer@dabbelt.com, tglx@linutronix.de, david@redhat.com, jannh@google.com, hughd@google.com, yuzhao@google.com, willy@infradead.org, muchun.song@linux.dev, vbabka@kernel.org, lorenzo.stoakes@oracle.com, akpm@linux-foundation.org, rientjes@google.com, vishal.moola@gmail.com, arnd@arndb.de, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, dave.hansen@linux.intel.com, rppt@kernel.org, ryan.roberts@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-csky@vger.kernel.org, linux-hexagon@vger.kernel.org, loongarch@lists.linux.dev, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-openrisc@vger.kernel.org, linux-sh@vger.kernel.org, linux-um@lists.infradead.org References: <0e8f0b3835c15e99145e0006ac1020ae45a2b166.1735549103.git.zhengqi.arch@bytedance.com> <1b09335c-f0b6-4ccb-9800-5fb22f7e8083@arm.com> <7e2c26c8-f5df-4833-a93f-3409b00b58fd@arm.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/1/3 17:13, Qi Zheng wrote: > > > On 2025/1/3 16:02, Kevin Brodsky wrote: >> On 03/01/2025 04:48, Qi Zheng wrote: >>> Hi Kevin, >>> >>> On 2025/1/3 00:53, Kevin Brodsky wrote: >>>> On 30/12/2024 10:07, Qi Zheng wrote: >>>>>    static inline void riscv_tlb_remove_ptdesc(struct mmu_gather *tlb, >>>>> void *pt) >>>>>    { >>>>> -    if (riscv_use_sbi_for_rfence()) >>>>> +    if (riscv_use_sbi_for_rfence()) { >>>>>            tlb_remove_ptdesc(tlb, pt); >>>>> -    else >>>>> +    } else { >>>>> +        pagetable_dtor(pt); >>>>>            tlb_remove_page_ptdesc(tlb, pt); >>>> >>>> I find the imbalance pretty confusing: pagetable_dtor() is called >>>> explicitly before using tlb_remove_page() but not tlb_remove_ptdesc(). >>>> Doesn't that assume that CONFIG_MMU_GATHER_HAVE_TABLE_FREE is selected? >>>> Could we not call pagetable_dtor() from >>>> __tlb_batch_free_encoded_pages() >>>> to ensure that the dtor is always called just before freeing, and >>>> remove >>> >>> In __tlb_batch_free_encoded_pages(), we can indeed detect PageTable() >>> and call pagetable_dtor() to dtor the page table pages. >>> But __tlb_batch_free_encoded_pages() is also used to free normal pages >>> (not page table pages), so I don't want to add overhead there. >> >> Interesting, can a tlb batch refer to pages than are not PTPs then? > > Yes, you can see the caller of __tlb_remove_folio_pages() or > tlb_remove_page_size(). > >> >>> >>> But now I think maybe we can do this in tlb_remove_page_ptdesc(), like >>> this: >>> >>> diff --git a/arch/csky/include/asm/pgalloc.h >>> b/arch/csky/include/asm/pgalloc.h >>> index f1ce5b7b28f22..e45c7e91dcbf9 100644 >>> --- a/arch/csky/include/asm/pgalloc.h >>> +++ b/arch/csky/include/asm/pgalloc.h >>> @@ -63,7 +63,6 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm) >>> >>>   #define __pte_free_tlb(tlb, pte, address)              \ >>>   do {                                                   \ >>> -       pagetable_dtor(page_ptdesc(pte));               \ >>>          tlb_remove_page_ptdesc(tlb, page_ptdesc(pte));  \ >>>   } while (0) >>> >>> [...] >>> >>> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h >>> index a96d4b440f3da..a59205863f431 100644 >>> --- a/include/asm-generic/tlb.h >>> +++ b/include/asm-generic/tlb.h >>> @@ -506,6 +506,7 @@ static inline void tlb_remove_ptdesc(struct >>> mmu_gather *tlb, void *pt) >>>   /* Like tlb_remove_ptdesc, but for page-like page directories. */ >>>   static inline void tlb_remove_page_ptdesc(struct mmu_gather *tlb, >>> struct ptdesc *pt) >>>   { >>> +       pagetable_dtor(pt); >>>          tlb_remove_page(tlb, ptdesc_page(pt)); >>>   } >> >> I think this is an interesting idea, it does make arch code easier to >> follow. OTOH it would have been more natural to me to call >> pagetable_dtor() from tlb_remove_page(). I can however see that this >> doesn't work, because tlb_remove_table() is defined as tlb_remove_page() >> if CONFIG_MMU_GATHER_HAVE_TABLE_FREE isn't selected. Which brings me >> back to my earlier question: in that case, aren't we missing a call to >> pagetable_dtor() when using tlb_remove_table() (or tlb_remove_ptdesc())? > > Thank you for pointing this out! > > Now, there are the following architectures selected > CONFIG_MMU_GATHER_RCU_TABLE_FREE: > > 1. arm: select MMU_GATHER_RCU_TABLE_FREE if SMP && ARM_LPAE > 2. arm64: select MMU_GATHER_RCU_TABLE_FREE > 3. powerpc: select MMU_GATHER_RCU_TABLE_FREE > 4. riscv: select MMU_GATHER_RCU_TABLE_FREE if SMP && MMU > 5. s390: select MMU_GATHER_RCU_TABLE_FREE > 6. sparc: select MMU_GATHER_RCU_TABLE_FREE if SMP > 7. x86: select MMU_GATHER_RCU_TABLE_FREE    if PARAVIRT > > If CONFIG_MMU_GATHER_TABLE_FREE is selected, an architecture is expected > to provide __tlb_remove_table(). This patch series modifies the > __tlb_remove_table() in arm, arm64, riscv, s390 and x86. Among them, > arm64 and s390 unconditionally select MMU_GATHER_RCU_TABLE_FREE, so we > only need to double-check arm, riscv and x86. > > For x86, it was called tlb_remove_page() in the non-PARAVIRT case, and I > added pagetable_dtor() for it explicitly (see patch #11), so this should > be no problem. > > For riscv, it will only call tlb_remove_ptdesc() in the case of > SMP && MMU, so this should be no problem. > > For arm, the call to pagetable_dtor() is indeed missed in the > non-MMU_GATHER_RCU_TABLE_FREE case. This needs to be fixed. But we > can't fix this by adding pagetable_dtor() to tlb_remove_table(), > because some architectures call tlb_remove_table() but don't support > page table statistics, like sparc. > > So a more direct fix might be: > > diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h > index a59205863f431..0a131444a18ca 100644 > --- a/include/asm-generic/tlb.h > +++ b/include/asm-generic/tlb.h > @@ -500,6 +500,9 @@ static inline void tlb_remove_page(struct mmu_gather > *tlb, struct page *page) > >  static inline void tlb_remove_ptdesc(struct mmu_gather *tlb, void *pt) >  { > +#ifndef CONFIG_MMU_GATHER_TABLE_FREE > +       pagetable_dtor(pt); > +#endif >         tlb_remove_table(tlb, pt); >  } > > Or fix it directly in arm? Like the following: > > diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h > index ea4fbe7b17f6f..cf5d0ca021440 100644 > --- a/arch/arm/include/asm/tlb.h > +++ b/arch/arm/include/asm/tlb.h > @@ -43,6 +43,9 @@ __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte, > unsigned long addr) >         __tlb_adjust_range(tlb, addr - PAGE_SIZE, 2 * PAGE_SIZE); >  #endif > > +#ifndef CONFIG_MMU_GATHER_TABLE_FREE > +       pagetable_dtor(ptdesc); > +#endif >         tlb_remove_ptdesc(tlb, ptdesc); >  } 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)) - -#endif /* CONFIG_MMU_GATHER_TABLE_FREE */ - #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE /* * This allows an architecture that does not use the linux page-tables for > > Thanks, > Qi > >> >> - Kevin