From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 07AE02517AF for ; Mon, 3 Mar 2025 16:30:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741019461; cv=none; b=Id9nQPtQadJSsO9M0zFjRt7ShbszoGg0CVCIDakqDSjvLCrzs0Hf/qadOwAWx7zr1H+KVbA1e33RTupM1q9f85LYose/zsL5ggSIB6UTsjxcqa7hHXz77Ieq97fnMhCyF3liwZAqzZMZ/h03ItLEcEhX1Ba+qmwK0ZfsmAuOdkk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741019461; c=relaxed/simple; bh=zwBWJQNiZElGf+tnFTiOyJan5xAOzuwmBeeeOxUUAKM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=r53YTwX+uZVwMDbvkRuO6eR4p7jLsA/feGFva60Pt4IbAmtND+f7S/JqHOtlJ3p2dkXRRr+f7OBVgNL4KYQQu/+naIx/9BuKe8QlpiJJuUldvD/X8WYf+k33pvfupRAoI+LXQL6owxlYmnx5JOsz0gutGx1NrXb/Ci2mQA1wvk8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=A9OVuhzc; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="A9OVuhzc" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1741019459; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=azxC6HZJ9nBU2F+f5yWV4gQ6J7sT6YtNWxk4WN8FkrY=; b=A9OVuhzcVM6agi3kRqlbRmgmTtQnZAbWNMviaarCoBPg8KwAyORpVDXJSJk1HpXBkvsTqe ZZwW6xBRV8NS9MnIWfrgv6VPKDWQv/R8xCEkyW7QLmTEU3o+jiXxXgt9nK8molqYRCRRLh PMIH+Zefww80fyZcJ605QcXUCjnCcVo= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-320-8sPY6Ya6PqCrRhJ2O6dnxg-1; Mon, 03 Mar 2025 11:30:53 -0500 X-MC-Unique: 8sPY6Ya6PqCrRhJ2O6dnxg-1 X-Mimecast-MFC-AGG-ID: 8sPY6Ya6PqCrRhJ2O6dnxg_1741019452 Received: by mail-wr1-f72.google.com with SMTP id ffacd0b85a97d-390df5962e1so2268868f8f.0 for ; Mon, 03 Mar 2025 08:30:52 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1741019452; x=1741624252; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=azxC6HZJ9nBU2F+f5yWV4gQ6J7sT6YtNWxk4WN8FkrY=; b=QvAxCim+0iIVHh5EJI7FfaD/u1J198/g69AKkdN5uaw4W+GfWgTfa5YjA3eiM8cgL3 zGO/59BtYxlQ8c6Q9nrqViWtXgHrca1AL6eGsyfxRS1fo09F2Pm0dNzRyJYlU3N2rIbl z6IPrHRoGdFfQlZTRcrCOprL5MsBlpIg1qb3ddUgwcxDCnrPMlaynUyuMfj2jufNdyAa Gxc9vuBVLZ/pKo8kbwAZt21X/SmQqGSHGg6e30GoOeptn68VXxWh1RNvjnuS6tRLZLxS Eukj0SYCT7OvDiD0VTjIUiaq7xrFntnXMgIpyMBbx+rku1ZSBcH1O6DIgUywNp0lGwLt Usiw== X-Gm-Message-State: AOJu0Ywn+nhmvEDWtK9bbsD7V4HkyKI3fEJYpzirw/IIAMKsRge/iJfe ufuLkumNeM8JoahGZiQ9Jne5x2UfEuZ8qO3B2SekT2nXFstdCjB/Zcv2x94ffDRUdEttGYJWVsc VQb2qt9Kz9UCu0icNTOSL9idGKmpoHoVFvRyhHmnBRoUmGHl0ETzvisy7HmxGrFX6RAU89aQL7j XIu0xjZUh9RtQ9iBih3fQK8kVtKb5qvyHblEfjRWt3+z96 X-Gm-Gg: ASbGnctEbXnPpA/vG+LFyIaK0s0UASQD/xVh4ToCRYRBfwYZjsySg5SVPscv6AzXWzH Opf9UVUpuB8QwEoaKUuU2Njx58CKP5+AhHE8Tq4jMTb9UwNf7qSDORt8paEJKJetrUnVotEZLNG iiHSONjqeGtAu0DBI9ohFD2W3TOo6yQlijeDQM8KsekflgMO5CMF/TKA54FQ1KcWE8/gfhxjj1j syi0gLXDKBuvc1Jx/ekQqOdTMIRX7jvl3XTpok76HtZhYSSxynRaTtMi0Q1V4EoPQn+IwrBMEx3 cc868PLpeS1eVasQFdBGVjRUGXtjZZBa5eiYagzDjxQfo/2Bt8nqYz2XMkVhi3/XcfqJGxaUCLA T X-Received: by 2002:a05:600c:5585:b0:43b:bedc:fcf6 with SMTP id 5b1f17b1804b1-43bbedcfe47mr44358665e9.1.1741019451794; Mon, 03 Mar 2025 08:30:51 -0800 (PST) X-Google-Smtp-Source: AGHT+IFzQb6PWhSpsnKcZbPTy2ai+36EkVbTPhZ8phSQIWx5xoPi2ki+HFSKpKKxfbHb4k7pKztumg== X-Received: by 2002:a05:600c:5585:b0:43b:bedc:fcf6 with SMTP id 5b1f17b1804b1-43bbedcfe47mr44358005e9.1.1741019451351; Mon, 03 Mar 2025 08:30:51 -0800 (PST) Received: from localhost (p200300cbc7349600af274326a2162bfb.dip0.t-ipconnect.de. [2003:cb:c734:9600:af27:4326:a216:2bfb]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-43b736f74e8sm172202265e9.7.2025.03.03.08.30.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Mar 2025 08:30:50 -0800 (PST) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org, David Hildenbrand , Andrew Morton , "Matthew Wilcox (Oracle)" , Tejun Heo , Zefan Li , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn Subject: [PATCH v3 15/20] mm: CONFIG_NO_PAGE_MAPCOUNT to prepare for not maintain per-page mapcounts in large folios Date: Mon, 3 Mar 2025 17:30:08 +0100 Message-ID: <20250303163014.1128035-16-david@redhat.com> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250303163014.1128035-1-david@redhat.com> References: <20250303163014.1128035-1-david@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit We're close to the finishing line: let's introduce a new CONFIG_NO_PAGE_MAPCOUNT config option where we will incrementally remove any dependencies on per-page mapcounts in large folios. Once that's done, we'll stop maintaining the per-page mapcounts with this config option enabled. CONFIG_NO_PAGE_MAPCOUNT will be EXPERIMENTAL for now, as we'll have to learn about some of the real world impact of some of the implications. As writing "!CONFIG_NO_PAGE_MAPCOUNT" is really nasty, let's introduce a helper config option "CONFIG_PAGE_MAPCOUNT" that expresses the negation. Signed-off-by: David Hildenbrand --- mm/Kconfig | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/mm/Kconfig b/mm/Kconfig index 4034a0441f650..e4bdcf11d1b86 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -881,8 +881,25 @@ config READ_ONLY_THP_FOR_FS support of file THPs will be developed in the next few release cycles. +config NO_PAGE_MAPCOUNT + bool "No per-page mapcount (EXPERIMENTAL)" + help + Do not maintain per-page mapcounts for pages part of larger + allocations, such as transparent huge pages. + + When this config option is enabled, some interfaces that relied on + this information will rely on less-precise per-allocation information + instead: for example, using the average per-page mapcount in such + a large allocation instead of the per-page mapcount. + + EXPERIMENTAL because the impact of some changes is still unclear. + endif # TRANSPARENT_HUGEPAGE +# simple helper to make the code a bit easier to read +config PAGE_MAPCOUNT + def_bool !NO_PAGE_MAPCOUNT + # # The architecture supports pgtable leaves that is larger than PAGE_SIZE # -- 2.48.1