Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757673AbcCaXGx (ORCPT ); Thu, 31 Mar 2016 19:06:53 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:38449 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752003AbcCaXGw (ORCPT ); Thu, 31 Mar 2016 19:06:52 -0400 Date: Thu, 31 Mar 2016 16:06:50 -0700 From: Andrew Morton To: Steve Capper Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, will.deacon@arm.com, dwoods@mellanox.com, mhocko@suse.com, mingo@kernel.org, "Kirill A. Shutemov" Subject: Re: [PATCH] mm: Exclude HugeTLB pages from THP page_mapped logic Message-Id: <20160331160650.cfc0fa57e97a45e94bc023f4@linux-foundation.org> In-Reply-To: <1459269581-21190-1-git-send-email-steve.capper@arm.com> References: <1459269581-21190-1-git-send-email-steve.capper@arm.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4882 Lines: 155 On Tue, 29 Mar 2016 17:39:41 +0100 Steve Capper wrote: > HugeTLB pages cannot be split, thus use the compound_mapcount to > track rmaps. > > Currently the page_mapped function will check the compound_mapcount, but s/the page_mapped function/page_mapped()/. It's so much simpler! > will also go through the constituent pages of a THP compound page and > query the individual _mapcount's too. > > Unfortunately, the page_mapped function does not distinguish between > HugeTLB and THP compound pages and assumes that a compound page always > needs to have HPAGE_PMD_NR pages querying. > > For most cases when dealing with HugeTLB this is just inefficient, but > for scenarios where the HugeTLB page size is less than the pmd block > size (e.g. when using contiguous bit on ARM) this can lead to crashes. > > This patch adjusts the page_mapped function such that we skip the > unnecessary THP reference checks for HugeTLB pages. > > Fixes: e1534ae95004 ("mm: differentiate page_mapped() from page_mapcount() for compound pages") > Cc: Kirill A. Shutemov > Signed-off-by: Steve Capper > --- > > Hi, > > This patch is my approach to fixing a problem that unearthed with > HugeTLB pages on arm64. We ran with PAGE_SIZE=64KB and placed down 32 > contiguous ptes to create 2MB HugeTLB pages. (We can provide hints to > the MMU that page table entries are contiguous thus larger TLB entries > can be used to represent them). So which kernel version(s) need this patch? I think both 4.4 and 4.5 will crash in this manner? Should we backport the fix into 4.4.x and 4.5.x? > > ... > > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1031,6 +1031,8 @@ static inline bool page_mapped(struct page *page) > page = compound_head(page); > if (atomic_read(compound_mapcount_ptr(page)) >= 0) > return true; > + if (PageHuge(page)) > + return false; > for (i = 0; i < hpage_nr_pages(page); i++) { > if (atomic_read(&page[i]._mapcount) >= 0) > return true; page_mapped() is moronically huge. Uninlining it saves 206 bytes per callsite. It has 40+ callsites. btw, is anyone else seeing this `make M=' breakage? akpm3:/usr/src/25> make M=mm Makefile:679: Cannot use CONFIG_KCOV: -fsanitize-coverage=trace-pc is not supported by compiler WARNING: Symbol version dump ./Module.symvers is missing; modules will have no dependencies and modversions. make[1]: *** No rule to make target `mm/filemap.o', needed by `mm/built-in.o'. Stop. make: *** [_module_mm] Error 2 It's a post-4.5 thing. From: Andrew Morton Subject: mm: uninline page_mapped() It's huge. Uninlining it saves 206 bytes per callsite. Shaves 4924 bytes from the x86_64 allmodconfig vmlinux. Cc: Steve Capper Cc: Kirill A. Shutemov Signed-off-by: Andrew Morton --- include/linux/mm.h | 21 +-------------------- mm/util.c | 22 ++++++++++++++++++++++ 2 files changed, 23 insertions(+), 20 deletions(-) diff -puN include/linux/mm.h~mm-uninline-page_mapped include/linux/mm.h --- a/include/linux/mm.h~mm-uninline-page_mapped +++ a/include/linux/mm.h @@ -1019,26 +1019,7 @@ static inline pgoff_t page_file_index(st return page->index; } -/* - * Return true if this page is mapped into pagetables. - * For compound page it returns true if any subpage of compound page is mapped. - */ -static inline bool page_mapped(struct page *page) -{ - int i; - if (likely(!PageCompound(page))) - return atomic_read(&page->_mapcount) >= 0; - page = compound_head(page); - if (atomic_read(compound_mapcount_ptr(page)) >= 0) - return true; - if (PageHuge(page)) - return false; - for (i = 0; i < hpage_nr_pages(page); i++) { - if (atomic_read(&page[i]._mapcount) >= 0) - return true; - } - return false; -} +bool page_mapped(struct page *page); /* * Return true only if the page has been allocated with diff -puN mm/util.c~mm-uninline-page_mapped mm/util.c --- a/mm/util.c~mm-uninline-page_mapped +++ a/mm/util.c @@ -346,6 +346,28 @@ void *page_rmapping(struct page *page) return __page_rmapping(page); } +/* + * Return true if this page is mapped into pagetables. + * For compound page it returns true if any subpage of compound page is mapped. + */ +bool page_mapped(struct page *page) +{ + int i; + if (likely(!PageCompound(page))) + return atomic_read(&page->_mapcount) >= 0; + page = compound_head(page); + if (atomic_read(compound_mapcount_ptr(page)) >= 0) + return true; + if (PageHuge(page)) + return false; + for (i = 0; i < hpage_nr_pages(page); i++) { + if (atomic_read(&page[i]._mapcount) >= 0) + return true; + } + return false; +} +EXPORT_SYMBOL(page_mapped); + struct anon_vma *page_anon_vma(struct page *page) { unsigned long mapping; _