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Wed, 05 Dec 2018 01:15:45 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id wB51Fiaa030611 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 5 Dec 2018 01:15:44 GMT Received: from abhmp0002.oracle.com (abhmp0002.oracle.com [141.146.116.8]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id wB51FhcR028012; Wed, 5 Dec 2018 01:15:44 GMT Received: from [10.39.243.186] (/10.39.243.186) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 04 Dec 2018 17:15:43 -0800 Subject: Re: [PATCH] /proc/kpagecount: return 0 for special pages that are never mapped To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, adobriyan@gmail.com, akpm@linux-foundation.org, vbabka@suse.cz, sfr@canb.auug.org.au, kirill.shutemov@linux.intel.com, rppt@linux.vnet.ibm.com, mhocko@suse.com, alexander.h.duyck@linux.intel.com, hannes@cmpxchg.org, miles.chen@mediatek.com, n-horiguchi@ah.jp.nec.com References: <1543963526-27917-1-git-send-email-anthony.yznaga@oracle.com> <20181205004836.GU10377@bombadil.infradead.org> From: anthony.yznaga@oracle.com Organization: Oracle Corporation Message-ID: Date: Tue, 4 Dec 2018 17:18:32 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181205004836.GU10377@bombadil.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9097 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1812050009 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/04/2018 04:48 PM, Matthew Wilcox wrote: > On Tue, Dec 04, 2018 at 02:45:26PM -0800, Anthony Yznaga wrote: >> Certain pages that are never mapped to userspace have a type >> indicated in the page_type field of their struct pages (e.g. PG_buddy). >> page_type overlaps with _mapcount so set the count to 0 and avoid >> calling page_mapcount() for these pages. >> >> Signed-off-by: Anthony Yznaga >> --- >> fs/proc/page.c | 2 +- >> include/linux/page-flags.h | 7 +++++++ >> 2 files changed, 8 insertions(+), 1 deletion(-) >> >> diff --git a/fs/proc/page.c b/fs/proc/page.c >> index 6c517b11acf8..40b05e0d4274 100644 >> --- a/fs/proc/page.c >> +++ b/fs/proc/page.c >> @@ -46,7 +46,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, >> ppage = pfn_to_page(pfn); >> else >> ppage = NULL; >> - if (!ppage || PageSlab(ppage)) >> + if (!ppage || PageSlab(ppage) || page_has_type(ppage)) >> pcount = 0; >> else >> pcount = page_mapcount(ppage); >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h >> index 50ce1bddaf56..f9a1c50ccefc 100644 >> --- a/include/linux/page-flags.h >> +++ b/include/linux/page-flags.h >> @@ -673,10 +673,17 @@ static inline int TestClearPageDoubleMap(struct page *page) >> #define PG_balloon 0x00000100 >> #define PG_kmemcg 0x00000200 >> #define PG_table 0x00000400 >> +#define PAGE_TYPE_ALL (PG_buddy | PG_balloon | PG_kmemcg | PG_table) >> >> #define PageType(page, flag) \ >> ((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE) >> >> +static inline int page_has_type(struct page *page) >> +{ >> + return (PageType(page, 0) && >> + ((page->page_type & PAGE_TYPE_ALL) != PAGE_TYPE_ALL)); >> +} >> + >> #define PAGE_TYPE_OPS(uname, lname) \ > I think this is a bit complex, and a bit of a pain to update as we add > new page types. How about this? > > return (int)page_type < -128; > > (I'm open to appropriate #defines to make this more obvious that it's ~0x7F) I thought about having this: #define PAGE_TYPE_END    0xffffff80 static int inline page_has_type(struct page *page) {     return page->page_type > PAGE_TYPE_BASE &&            page->page_type < PAGE_TYPE_END; } But I opted for the additional complexity to avoid more false-positives from possibly corrupted values.  I'm certainly fine with a simple approach, though.