From nobody Fri Dec 19 06:16:34 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 242791B6528 for ; Thu, 29 Aug 2024 16:59:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724950767; cv=none; b=Zv7OFEcZK07q6RSSGomS4eFQij/oy/QgO7O4vS5y1jZvl8n3gE8BoKroacC6SDBhtX/+OovbScB5WGbYvKhxg3TV3jNI8qQyUSGMQFPjzr79N12i4/pL8AHxpILzYS6VQscJHO/I57U+mGj12A8tmIXwV4z+m4wbv3lhNCKUfwc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724950767; c=relaxed/simple; bh=2kZ7QGLHXwtMIchnMAYhCynmld3eYgcPA3qlbJ9RCfE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=I+CI7qxxPH2gpmUi6kILhShvhlMIs6cMoCD1PtjMDQ4BPuJPOibtXaspTG0x0CEpTXVs4m5gzhpTyuA1uyB1IoDRTAtR5HlcMoRAsvNsBEI230tQbih3E5J4Aqhe/tb9cWMknm+HhHTVfTZE8TaZdCfnIn5oywpZASq6k2JBvNs= 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=hp2uUa3q; arc=none smtp.client-ip=170.10.129.124 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="hp2uUa3q" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1724950765; 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=mZddLqrKBd43/r/px6zwJ3YX6SWmvbs5NWYNR2u4nCE=; b=hp2uUa3qOQXGIp3s8mAV5jUxMl0ABeltgXQNmatmcs1guWhxZGLyRlTt6nJ4KBeN2WB/MW lELXf8iL1uyp+ZjZkF5IPo5ocW3+KqiJjYSURR/QKVbmZ9e1qAJbk1TrNx9PYwVoCXRZug ZnxE4jA/QKvmgbZzMJDX3npujBKDW2A= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-481-IesVcwbKN1S5VOVmE03pWw-1; Thu, 29 Aug 2024 12:59:18 -0400 X-MC-Unique: IesVcwbKN1S5VOVmE03pWw-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 9B545196E0A8; Thu, 29 Aug 2024 16:59:16 +0000 (UTC) Received: from t14s.redhat.com (unknown [10.39.193.245]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 343891955F21; Thu, 29 Aug 2024 16:59:08 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, cgroups@vger.kernel.org, x86@kernel.org, linux-fsdevel@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 Subject: [PATCH v1 16/17] fs/proc/task_mmu: remove per-page mapcount dependency for smaps/smaps_rollup (CONFIG_NO_PAGE_MAPCOUNT) Date: Thu, 29 Aug 2024 18:56:19 +0200 Message-ID: <20240829165627.2256514-17-david@redhat.com> In-Reply-To: <20240829165627.2256514-1-david@redhat.com> References: <20240829165627.2256514-1-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: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Content-Type: text/plain; charset="utf-8" Let's implement an alternative when per-page mapcounts in large folios are no longer maintained -- soon with CONFIG_NO_PAGE_MAPCOUNT. When computing the output for smaps / smaps_rollups, in particular when calculating the USS (Unique Set Size) and the PSS (Proportional Set Size), we still rely on per-page mapcounts. To determine private vs. shared, we'll use folio_likely_mapped_shared(), similar to how we handle PM_MMAP_EXCLUSIVE. Similarly, we might now under-estimate the USS and count pages towards "shared" that are actually "private" ("exclusively mapped"). When calculating the PSS, we'll now also use the average per-page mapcount for large folios: this can result in both, an over-estimation and an under-estimation of the PSS. The difference is not expected to matter much in practice, but we'll have to learn as we go. We can now provide folio_precise_page_mapcount() only with CONFIG_PAGE_MAPCOUNT, and remove one of the last users of per-page mapcounts when CONFIG_NO_PAGE_MAPCOUNT is enabled. Document the new behavior. Signed-off-by: David Hildenbrand --- Documentation/filesystems/proc.rst | 13 +++++++++++++ fs/proc/internal.h | 2 ++ fs/proc/task_mmu.c | 17 +++++++++++++++-- 3 files changed, 30 insertions(+), 2 deletions(-) diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems= /proc.rst index bed03e77c0f91..7cbab4135f244 100644 --- a/Documentation/filesystems/proc.rst +++ b/Documentation/filesystems/proc.rst @@ -504,6 +504,19 @@ Note that even a page which is part of a MAP_SHARED ma= pping, but has only a single pte mapped, i.e. is currently used by only one process, is accou= nted as private and not as shared. =20 +Note that in some kernel configurations, all pages part of a larger alloca= tion +(e.g., THP) might be considered "shared" if the large allocation is +considered "shared": if not all pages are exclusive to the same process. +Further, some kernel configurations might consider larger allocations "sha= red", +if they were at one point considered "shared", even if they would now be +considered "exclusive". + +Some kernel configurations do not track the precise number of times a page= part +of a larger allocation is mapped. In this case, when calculating the PSS, = the +average number of mappings per page in this larger allocation might be used +as an approximation for the number of mappings of a page. The PSS calculat= ion +will be imprecise in this case. + "Referenced" indicates the amount of memory currently marked as referenced= or accessed. =20 diff --git a/fs/proc/internal.h b/fs/proc/internal.h index 3c687f97e18c4..8c9ef19526d2b 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -143,6 +143,7 @@ unsigned name_to_int(const struct qstr *qstr); /* Worst case buffer size needed for holding an integer. */ #define PROC_NUMBUF 13 =20 +#ifdef CONFIG_PAGE_MAPCOUNT /** * folio_precise_page_mapcount() - Number of mappings of this folio page. * @folio: The folio. @@ -173,6 +174,7 @@ static inline int folio_precise_page_mapcount(struct fo= lio *folio, =20 return mapcount; } +#endif /* CONFIG_PAGE_MAPCOUNT */ =20 /** * folio_average_page_mapcount() - Average number of mappings per page in = this diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 3d9fe99346478..30306e231ff04 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -734,6 +734,8 @@ static void smaps_account(struct mem_size_stats *mss, s= truct page *page, struct folio *folio =3D page_folio(page); int i, nr =3D compound ? compound_nr(page) : 1; unsigned long size =3D nr * PAGE_SIZE; + bool exclusive; + int mapcount; =20 /* * First accumulate quantities that depend only on |size| and the type @@ -774,18 +776,29 @@ static void smaps_account(struct mem_size_stats *mss,= struct page *page, dirty, locked, present); return; } + +#ifndef CONFIG_PAGE_MAPCOUNT + mapcount =3D folio_average_page_mapcount(folio); + exclusive =3D !folio_likely_mapped_shared(folio); +#endif + /* * We obtain a snapshot of the mapcount. Without holding the folio lock * this snapshot can be slightly wrong as we cannot always read the * mapcount atomically. */ for (i =3D 0; i < nr; i++, page++) { - int mapcount =3D folio_precise_page_mapcount(folio, page); unsigned long pss =3D PAGE_SIZE << PSS_SHIFT; + +#ifdef CONFIG_PAGE_MAPCOUNT + mapcount =3D folio_precise_page_mapcount(folio, page); + exclusive =3D mapcount < 2; +#endif + if (mapcount >=3D 2) pss /=3D mapcount; smaps_page_accumulate(mss, folio, PAGE_SIZE, pss, - dirty, locked, mapcount < 2); + dirty, locked, exclusive); } } =20 --=20 2.46.0