From patchwork Thu Aug 29 16:56:16 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13783468 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 C8EDD1B81DB for ; Thu, 29 Aug 2024 16:59:00 +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=1724950742; cv=none; b=WVzlTr/o6q57N4bAZ/QbjT4bSNApFK6F9aXT7O3w1YhMQx0k1bYxIr4hS55iaTxyTbW/UpA/6dbA3ciE5tOF4OjBnvSVn3ufZdx8p5Jffjo69PiuYYWWW942GmeeflPWk1q30gXH4lNxXKcPlkbtkI/qte4VucBjB/6rZDaZNcI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724950742; c=relaxed/simple; bh=HNUw6L79YorAY7Er9IcXo5/0qoizTqeiSeFuYwU1AX8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=naa++6cmRE5NijOizhPOtZdJTb737wYgQeS7SPoe0feUTv9vxl1B3mN2jSgCZRr5bfD9o14FSQblp4JYa3i3mzwSBy/ptx6tKF9PBlXfrOyEK6k6ZroJkyuPOrNPg6Yq3kb/surprwB9B+mebiODjcmuIJQ/SgoK8LpdGrf05Jo= 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=MIDHBggJ; 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="MIDHBggJ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1724950740; 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=/4w50puZlu0HXrTGynq7fLz3hKXbxnRdIDDiKfwRwdI=; b=MIDHBggJjuRbN5jmkFDAYktU12AH0nDt/FqD1zLCI/Hl0v1nRWzFA7pUwrFtmjZeyTkNBZ S2L1hkq2E8/cVbAn25UGDffFn1+Wpu6mLnfPoVG14dlEnsruDEpQWhyYiQZTGvzYXMep1N xmRJrANuwDlVwQqw+ge6iFjpCobft3I= Received: from mx-prod-mc-03.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-251-I4RGjMuXNxC500-cFdsqyQ-1; Thu, 29 Aug 2024 12:58:55 -0400 X-MC-Unique: I4RGjMuXNxC500-cFdsqyQ-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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4912C18F498B; Thu, 29 Aug 2024 16:58:51 +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 1C0F81955F21; Thu, 29 Aug 2024 16:58:44 +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_Koutn=C3=BD?= , Jonathan Corbet , Andy Lutomirski , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen Subject: [PATCH v1 13/17] fs/proc/page: remove per-page mapcount dependency for /proc/kpagecount (CONFIG_NO_PAGE_MAPCOUNT) Date: Thu, 29 Aug 2024 18:56:16 +0200 Message-ID: <20240829165627.2256514-14-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-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Let's implement an alternative when per-page mapcounts in large folios are no longer maintained -- soon with CONFIG_NO_PAGE_MAPCOUNT. For large folios, we'll return the per-page average mapcount within the folio, except when the average is 0 but the folio is mapped: then we return 1. For hugetlb folios and for large folios that are fully mapped into all address spaces, there is no change. As an alternative, we could simply return 0 for non-hugetlb large folios, or disable this legacy interface with CONFIG_NO_PAGE_MAPCOUNT. But the information exposed by this interface can still be valuable, and frequently we deal with fully-mapped large folios where the average corresponds to the actual page mapcount. So we'll leave it like this for now and document the new behavior. Signed-off-by: David Hildenbrand --- Documentation/admin-guide/mm/pagemap.rst | 7 +++++- fs/proc/internal.h | 31 ++++++++++++++++++++++++ fs/proc/page.c | 18 +++++++++++--- 3 files changed, 52 insertions(+), 4 deletions(-) diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst index caba0f52dd36c..49590306c61a0 100644 --- a/Documentation/admin-guide/mm/pagemap.rst +++ b/Documentation/admin-guide/mm/pagemap.rst @@ -42,7 +42,12 @@ There are four components to pagemap: skip over unmapped regions. * ``/proc/kpagecount``. This file contains a 64-bit count of the number of - times each page is mapped, indexed by PFN. + times each page is mapped, indexed by PFN. Some kernel configurations do + not track the precise number of times a page part of a larger allocation + (e.g., THP) is mapped. In these configurations, the average number of + mappings per page in this larger allocation is returned instead. However, + if any page of the large allocation is mapped, the returned value will + be at least 1. The page-types tool in the tools/mm directory can be used to query the number of times a page is mapped. diff --git a/fs/proc/internal.h b/fs/proc/internal.h index cc520168f8b69..3c687f97e18c4 100644 --- a/fs/proc/internal.h +++ b/fs/proc/internal.h @@ -174,6 +174,37 @@ static inline int folio_precise_page_mapcount(struct folio *folio, return mapcount; } +/** + * folio_average_page_mapcount() - Average number of mappings per page in this + * folio + * @folio: The folio. + * + * The average number of present user page table entries that reference each + * page in this folio as tracked via the RMAP: either referenced directly + * (PTE) or as part of a larger area that covers this page (e.g., PMD). + * + * Returns: The average number of mappings per page in this folio. 0 for + * folios that are not mapped to user space or are not tracked via the RMAP + * (e.g., shared zeropage). + */ +static inline int folio_average_page_mapcount(struct folio *folio) +{ + int mapcount, entire_mapcount; + unsigned int adjust; + + if (!folio_test_large(folio)) + return atomic_read(&folio->_mapcount) + 1; + + mapcount = folio_large_mapcount(folio); + entire_mapcount = folio_entire_mapcount(folio); + if (mapcount <= entire_mapcount) + return entire_mapcount; + mapcount -= entire_mapcount; + + adjust = folio_large_nr_pages(folio) / 2; + return ((mapcount + adjust) >> folio_large_order(folio)) + + entire_mapcount; +} /* * array.c */ diff --git a/fs/proc/page.c b/fs/proc/page.c index a55f5acefa974..c7838de949287 100644 --- a/fs/proc/page.c +++ b/fs/proc/page.c @@ -67,9 +67,21 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, * memmaps that were actually initialized. */ page = pfn_to_online_page(pfn); - if (page) - mapcount = folio_precise_page_mapcount(page_folio(page), - page); + if (page) { + struct folio *folio = page_folio(page); + +#ifdef CONFIG_PAGE_MAPCOUNT + mapcount = folio_precise_page_mapcount(folio, page); +#else /* !CONFIG_PAGE_MAPCOUNT */ + /* + * Indicate the per-page average, but at least "1" for + * mapped folios. + */ + mapcount = folio_average_page_mapcount(folio); + if (!mapcount && folio_test_large(folio) && folio_mapped(folio)) + mapcount = 1; +#endif /* !CONFIG_PAGE_MAPCOUNT */ + } if (put_user(mapcount, out)) { ret = -EFAULT;