From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7B81D2367B5; Mon, 19 Jan 2026 10:12:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768817576; cv=none; b=qCTOsGN2EtkADfJupaUkiA6gApGdrSEi6SxHegZnBkhgWmYKvYYtkLCspIsVT5JKDTYp1G5hTs0ghCdVBO39GaO2ZJvWOTc1EKQNhlybL0aDBqCxQA3lVItOqMH1JtDeDDPYxiLXoaiTl0TmRQvNXJKTAtW5GKUDsVpkA/zNBX4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768817576; c=relaxed/simple; bh=JzYfQ2HAxs4i1+wCNZ4YJF2miFvaY77kYkNH822rrWs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KCFU9XG/Jlxk/3RA+TAtxFMXEkIf7beu58kg92zFuZwB0EpTSwbzkVj1M+7OhNwrTnioj1qJgvTr+yOGCHwQQrCj18vjp6gNfbwTGme2EMBFXJv+yxfh8Q4jclaFZmm/U/u42Iv1M+8dp33wEkwf7ft7AWcgs/q17GEOc8MSJYA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=me8+IGew; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="me8+IGew" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C7840C116C6; Mon, 19 Jan 2026 10:12:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768817576; bh=JzYfQ2HAxs4i1+wCNZ4YJF2miFvaY77kYkNH822rrWs=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=me8+IGewGCeffwxGVagl70q+hrSe2opYVeA1iGHPxfp3jOTyA5Mb5KeeLkc/Xja14 HfCoVgl4rWFfeV2WDNbJUF3aDkXBLFx+1M/3Kr8Mo/047Y4IUJprtnZUgHNC0AUUCr 89z9nS4T9hLB1/EnWTxzIbJhlH1HocGK/UMOIYYxqsRRynUaByy3bX0BWBcPAUw7sy WQneEXcH6ogG6xNS1YOTkZw8XHe0vetHdKxlkRbStzTvr/D+mbvAndI4gRQBd2SP9L aPNuojOPQ0OHFPjwXGaM7HxgAP5LamThIQoakceGGuilMqy4wQEx6wGMh8/64SuQCD mHUCpaQBpY2lA== Message-ID: <74607439-5f52-4c03-904f-01c675e8bb06@kernel.org> Date: Mon, 19 Jan 2026 11:12:50 +0100 Precedence: bulk X-Mailing-List: linux-alpha@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 7/7] mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE To: 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 Cc: 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 References: <24837e0e-db86-4c64-8387-243d94293b48@linux.dev> From: "David Hildenbrand (Red Hat)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/19/26 04:50, Qi Zheng wrote: > > > On 1/18/26 7:23 PM, David Hildenbrand (Red Hat) wrote: >> On 12/17/25 10:45, 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. >> >> This patch seems to make s390x compilations sometimes unhappy: >> >> Unverified Warning (likely false positive, kindly check if interested): > > I believe it is a false positive. > >> >>     mm/memory.c:1911 zap_pte_range() error: uninitialized symbol 'pmdval'. >> >> Warning ids grouped by kconfigs: >> >> recent_errors >> `-- s390-randconfig-r072-20260117 >>     `-- mm-memory.c-zap_pte_range()-error:uninitialized-symbol-pmdval-. >> >> I assume the compiler is not able to figure out that only when >> try_get_and_clear_pmd() returns false that pmdval could be uninitialized. >> >> Maybe it has to do with LTO? >> >> >> After all, that function resides in a different compilation unit. >> >> Which makes me wonder whether we want to just move try_get_and_clear_pmd() >> and reclaim_pt_is_enabled() to internal.h or even just memory.c? >> >> But then, maybe we could remove pt_reclaim.c completely and just have >> try_to_free_pte() in memory.c as well? >> >> >> I would just do the following cleanup: >> >> From cfe97092f71fcc88f729f07ee0bc6816e3e398f0 Mon Sep 17 00:00:00 2001 >> From: "David Hildenbrand (Red Hat)" >> Date: Sun, 18 Jan 2026 12:20:55 +0100 >> Subject: [PATCH] mm: move pte table reclaim code to memory.c >> >> Let's move the code and clean it up a bit along the way. >> >> Signed-off-by: David Hildenbrand (Red Hat) >> --- >>  MAINTAINERS     |  1 - >>  mm/internal.h   | 18 ------------- >>  mm/memory.c     | 70 ++++++++++++++++++++++++++++++++++++++++++----- >>  mm/pt_reclaim.c | 72 ------------------------------------------------- >>  4 files changed, 64 insertions(+), 97 deletions(-) >>  delete mode 100644 mm/pt_reclaim.c > > Make sense, and LGTM. The reason it was placed in mm/pt_reclaim.c before > was because there would be other paths calling these functions in the > future. However, it can be separated out or put into a header file when > there are actually such callers. Most relevant zapping better happens in memory.c :) There is, of course, zapping due to RMAP unmap, but that mostly targets individual PTEs, and not a complete pte table. Likely, if ever required, we should expose a proper zapping interface from memory.c to other users, assuming the existing one is not suitable. > > would you be willing to send out an official patch? Yes, I can send one out, thanks. -- Cheers David