From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759932AbcHaVak (ORCPT ); Wed, 31 Aug 2016 17:30:40 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:51385 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754873AbcHaVad (ORCPT ); Wed, 31 Aug 2016 17:30:33 -0400 Date: Wed, 31 Aug 2016 14:30:31 -0700 From: Andrew Morton To: Mel Gorman Cc: "Huang, Ying" , tim.c.chen@intel.com, dave.hansen@intel.com, andi.kleen@intel.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel , Tejun Heo , Wu Fengguang Subject: Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache Message-Id: <20160831143031.4e5a180f969ec6997637a96f@linux-foundation.org> In-Reply-To: <20160831091459.GY8119@techsingularity.net> References: <1472578089-5560-1-git-send-email-ying.huang@intel.com> <20160831091459.GY8119@techsingularity.net> 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 On Wed, 31 Aug 2016 10:14:59 +0100 Mel Gorman wrote: > > 2506952 __ 2% +28.1% 3212076 __ 7% vm-scalability.throughput > > 1207402 __ 7% +22.3% 1476578 __ 6% vmstat.swap.so > > 10.86 __ 12% -23.4% 8.31 __ 16% perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list > > 10.82 __ 13% -33.1% 7.24 __ 14% perf-profile.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_zone_memcg > > 10.36 __ 11% -100.0% 0.00 __ -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page.__swap_writepage.swap_writepage > > 10.52 __ 12% -100.0% 0.00 __ -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writeback.page_endio.pmem_rw_page > > > > I didn't see anything wrong with the patch but it's worth highlighting > that this hunk means we are now out of GFP bits. Well ugh. What are we to do about that? Sigh. This? From: Andrew Morton Subject: mm: check that we haven't used more than 32 bits in address_space.flags After "mm: don't use radix tree writeback tags for pages in swap cache", all the flags are now used up on 32-bit builds. Add a build-time assertion to prevent 64-bit developers from accidentally breaking things. Cc: Mel Gorman Cc: "Huang, Ying" Signed-off-by: Andrew Morton --- include/linux/pagemap.h | 2 ++ init/main.c | 4 ++++ 2 files changed, 6 insertions(+) diff -puN include/linux/pagemap.h~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags include/linux/pagemap.h --- a/include/linux/pagemap.h~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags +++ a/include/linux/pagemap.h @@ -27,6 +27,8 @@ enum mapping_flags { AS_EXITING = __GFP_BITS_SHIFT + 4, /* final truncate in progress */ /* writeback related tags are not used */ AS_NO_WRITEBACK_TAGS = __GFP_BITS_SHIFT + 5, + + AS_LAST_FLAG, }; static inline void mapping_set_error(struct address_space *mapping, int error) diff -puN init/main.c~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags init/main.c --- a/init/main.c~mm-check-that-we-havent-used-more-than-32-bits-in-address_spaceflags +++ a/init/main.c @@ -59,6 +59,7 @@ #include #include #include +#include #include #include #include @@ -463,6 +464,9 @@ void __init __weak thread_stack_cache_in */ static void __init mm_init(void) { + /* Does address_space.flags still fit into a 32-bit ulong? */ + BUILD_BUG_ON(AS_LAST_FLAG > 32); + /* * page_ext requires contiguous pages, * bigger than MAX_ORDER unless SPARSEMEM. _