From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 01D46CED617 for ; Tue, 18 Nov 2025 12:03:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=YSfDkQJHByC5W64S3r1RZBfV7l+QzHRtZt5IkHkWjXM=; b=nl0zqo1hIkRMQeq9zrfM+k7G0h i+r/9MRo3050Rq+JUrZvd8ySwbMG+fN8algrxjJNpAO9mu7ompYmNRFwsZDAL2jN1aLOOqHLHgfrw MshtY6zgD34B7KpIBKFTS7l3zicrJRsN9Urw93ZGXN+jCYYmH7E0gPYjgKqHqhRGBDF72KS4eMSqc RN4OLnWSm6IPkG3mODVLiFhUIghaLKt/RUj3igAz2Is1BfyHpA+LsFX5wUt5fd85F1RG4Rc5cdCFw p/mgd7oL49LIsGa2rBaQEXUaace2ImDpJwBwCFCIKKAZ2OnMMmJ0/DAPAdDC15n/Divcl+Gu0Qfig ok4zvwVw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vLKR8-00000000NRo-3tA9; Tue, 18 Nov 2025 12:03:54 +0000 Received: from out-179.mta1.migadu.com ([95.215.58.179]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vLKR6-00000000NQm-20tn for linux-um@lists.infradead.org; Tue, 18 Nov 2025 12:03:53 +0000 Message-ID: <195baf7c-1f4e-46a4-a4aa-e68e7d00c0f9@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1763467417; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YSfDkQJHByC5W64S3r1RZBfV7l+QzHRtZt5IkHkWjXM=; b=Z9Rbcq7i2Y1LGHCoUGuTi6ppSLunSulmRKUQ4pjayjy42viyJ+DcXrTYmImrfSRJw+UKR4 UVTRGLFHLTlNdVaXnjT3ixLkagqhNZyq0Aqov/I7FCpMijq/fe4cVtkKv+q+YaHP5txxbN qqqQe//KpgfJbRYA+2BGf/imvJ4aYQ4= Date: Tue, 18 Nov 2025 20:02:30 +0800 MIME-Version: 1.0 Subject: Re: [PATCH 7/7] mm: make PT_RECLAIM depend on MMU_GATHER_RCU_TABLE_FREE && 64BIT To: "David Hildenbrand (Red Hat)" , will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, dev.jain@arm.com, akpm@linux-foundation.org, ioworker0@gmail.com Cc: linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-um@lists.infradead.org, Qi Zheng References: <0a4d1e6f0bf299cafd1fc624f965bd1ca542cea8.1763117269.git.zhengqi.arch@bytedance.com> <355d3bf3-c6bc-403e-9f19-89259d868611@kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: <355d3bf3-c6bc-403e-9f19-89259d868611@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251118_040352_656987_36D5E449 X-CRM114-Status: GOOD ( 17.75 ) 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: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On 11/18/25 12:57 AM, David Hildenbrand (Red Hat) wrote: > On 14.11.25 12:11, Qi Zheng wrote: >> From: Qi Zheng > > Subject: s/&&/&/ will do. > >> >> Make PT_RECLAIM depend on MMU_GATHER_RCU_TABLE_FREE so that PT_RECLAIM >> can >> be enabled by default on all architectures that support >> MMU_GATHER_RCU_TABLE_FREE. >> >> Considering that a large number of PTE page table pages (such as 100GB+) >> can only be caused on a 64-bit system, let PT_RECLAIM also depend on >> 64BIT. >> >> Signed-off-by: Qi Zheng >> --- >>   arch/x86/Kconfig | 1 - >>   mm/Kconfig       | 6 +----- >>   2 files changed, 1 insertion(+), 6 deletions(-) >> >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig >> index eac2e86056902..96bff81fd4787 100644 >> --- a/arch/x86/Kconfig >> +++ b/arch/x86/Kconfig >> @@ -330,7 +330,6 @@ 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 a5a90b169435d..e795fbd69e50c 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -1440,14 +1440,10 @@ 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 >> +    depends on MMU_GATHER_RCU_TABLE_FREE && MMU && SMP && 64BIT > > Who would we have MMU_GATHER_RCU_TABLE_FREE without MMU? (can we drop > the MMU part) OK. > > Why do we care about SMP in the first place? (can we frop SMP) OK. > > But I also wonder why we need "MMU_GATHER_RCU_TABLE_FREE && 64BIT": > > Would it be harmful on 32bit (sure, we might not reclaim as much, but > still there is memory to be reclaimed?)? This is also fine on 32bit, but the benefits are not significant, So I chose to enable it only on 64-bit. I actually tried enabling MMU_GATHER_RCU_TABLE_FREE on all architectures, and apart from sparc32 being a bit troublesome (because it uses mm->page_table_lock for synchronization within __pte_free_tlb()), the modifications were relatively simple. > > If all 64BIT support MMU_GATHER_RCU_TABLE_FREE (as you previously > state), why can't we only check for 64BIT? OK, will do. Thanks, Qi >