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dev.jain@arm.com, akpm@linux-foundation.org, david@kernel.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: <20260101020715.45wqnjgcklvjcth3@master> Reply-To: Wei Yang References: <20251231094243.zmjs7kgflm7q6k73@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-Rspamd-Server: rspam02 X-Stat-Signature: eumae6fyri9ya4uzuqr56qhff4zq15hj X-Rspam-User: X-Rspamd-Queue-Id: 71B6C40004 X-HE-Tag: 1767233238-532775 X-HE-Meta: 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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? >> >> Thanks in advance for your explanation. >> >> -- Wei Yang Help you, Help me