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Thu, 22 Jan 2026 06:00:35 -0800 (PST) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b884006d3bbsm68748466b.32.2026.01.22.06.00.34 (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Thu, 22 Jan 2026 06:00:35 -0800 (PST) Date: Thu, 22 Jan 2026 14:00:34 +0000 From: Wei Yang To: "David Hildenbrand (Red Hat)" Cc: Wei Yang , Qi Zheng , will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, dev.jain@arm.com, akpm@linux-foundation.org, ioworker0@gmail.com, linmag7@gmail.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-alpha@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-um@lists.infradead.org, Qi Zheng Subject: Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE Message-ID: <20260122140034.ymigrfppzwvmcjkr@master> References: <20251231094243.zmjs7kgflm7q6k73@master> <20260101020715.45wqnjgcklvjcth3@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170113 (1.7.2) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260122_060039_081474_67C6015E X-CRM114-Status: GOOD ( 33.97 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Wei Yang Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On Mon, Jan 19, 2026 at 11:18:52AM +0100, David Hildenbrand (Red Hat) wrote: >On 1/1/26 03:07, Wei Yang wrote: >> On Wed, Dec 31, 2025 at 05:52:57PM +0800, Qi Zheng wrote: >> > >> > >> > On 12/31/25 5:42 PM, Wei Yang wrote: >> > > On Wed, Dec 17, 2025 at 05:45:48PM +0800, Qi Zheng wrote: >> > > > From: Qi Zheng >> > > > >> > > > The PT_RECLAIM can work on all architectures that support >> > > > MMU_GATHER_RCU_TABLE_FREE, so make PT_RECLAIM depends on >> > > > MMU_GATHER_RCU_TABLE_FREE. >> > > > >> > > > BTW, change PT_RECLAIM to be enabled by default, since nobody should want >> > > > to turn it off. >> > > > >> > > > Signed-off-by: Qi Zheng >> > > > --- >> > > > arch/x86/Kconfig | 1 - >> > > > mm/Kconfig | 9 ++------- >> > > > 2 files changed, 2 insertions(+), 8 deletions(-) >> > > > >> > > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> > > > index 80527299f859a..0d22da56a71b0 100644 >> > > > --- a/arch/x86/Kconfig >> > > > +++ b/arch/x86/Kconfig >> > > > @@ -331,7 +331,6 @@ config X86 >> > > > select FUNCTION_ALIGNMENT_4B >> > > > imply IMA_SECURE_AND_OR_TRUSTED_BOOT if EFI >> > > > select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE >> > > > - select ARCH_SUPPORTS_PT_RECLAIM if X86_64 >> > > > select ARCH_SUPPORTS_SCHED_SMT if SMP >> > > > select SCHED_SMT if SMP >> > > > select ARCH_SUPPORTS_SCHED_CLUSTER if SMP >> > > > diff --git a/mm/Kconfig b/mm/Kconfig >> > > > index bd0ea5454af82..fc00b429b7129 100644 >> > > > --- a/mm/Kconfig >> > > > +++ b/mm/Kconfig >> > > > @@ -1447,14 +1447,9 @@ config ARCH_HAS_USER_SHADOW_STACK >> > > > The architecture has hardware support for userspace shadow call >> > > > stacks (eg, x86 CET, arm64 GCS or RISC-V Zicfiss). >> > > > >> > > > -config ARCH_SUPPORTS_PT_RECLAIM >> > > > - def_bool n >> > > > - >> > > > config PT_RECLAIM >> > > > - bool "reclaim empty user page table pages" >> > > > - default y >> > > > - depends on ARCH_SUPPORTS_PT_RECLAIM && MMU && SMP >> > > > - select MMU_GATHER_RCU_TABLE_FREE >> > > > + def_bool y >> > > > + depends on MMU_GATHER_RCU_TABLE_FREE >> > > > help >> > > > Try to reclaim empty user page table pages in paths other than munmap >> > > > and exit_mmap path. >> > > >> > > Hi, Qi >> > > >> > > I am new to PT_RECLAIM, when reading related code I got one question. >> > > >> > > Before this patch, we could have this config combination: >> > > >> > > CONFIG_MMU_GATHER_RCU_TABLE_FREE & !CONFIG_PT_RECLAIM >> > > >> > > This means tlb_remove_table_free() is rcu version while tlb_remove_table_one() >> > > is semi rcu version. >> > > >> > > I am curious could we use rcu version tlb_remove_table_one() for this case? >> > > Use rcu version tlb_remove_table_one() if CONFIG_MMU_GATHER_RCU_TABLE_FREE. Is >> > > there some limitation here? >> > >> > I think there's no problem. The rcu version can also ensure that the >> > fast GUP works well. >> > >> >> Thanks for your quick response :-) >> >> And Happy New Year >> >> So my little suggestion is move the definition of __tlb_remove_table_one() >> under CONFIG_MMU_GATHER_RCU_TABLE_FREE. Do you thinks this would be more >> clear? > > >Do you mean > >diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c >index 2faa23d7f8d42..6aeba4bae68d2 100644 >--- a/mm/mmu_gather.c >+++ b/mm/mmu_gather.c >@@ -319,7 +319,7 @@ static inline void tlb_table_invalidate(struct mmu_gather >*tlb) > } > } > >-#ifdef CONFIG_PT_RECLAIM >+#ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE > static inline void __tlb_remove_table_one_rcu(struct rcu_head *head) > { > struct ptdesc *ptdesc; > >? Sorry for the late reply. Yes, and maybe we can move the definition to the #ifdef CONFIG_MMU_GATHER_RCU_TABLE_FREE code block above, then to be next to tlb_remove_table_free(). So that we always have rcu version when CONFIG_MMU_GATHER_RCU_TABLE_FREE. > >-- >Cheers > >David -- Wei Yang Help you, Help me