From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:59870 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725905AbeLEAsk (ORCPT ); Tue, 4 Dec 2018 19:48:40 -0500 Date: Tue, 4 Dec 2018 16:48:36 -0800 From: Matthew Wilcox To: Anthony Yznaga 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 Subject: Re: [PATCH] /proc/kpagecount: return 0 for special pages that are never mapped Message-ID: <20181205004836.GU10377@bombadil.infradead.org> References: <1543963526-27917-1-git-send-email-anthony.yznaga@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1543963526-27917-1-git-send-email-anthony.yznaga@oracle.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: 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)