From: Michal Hocko Subject: Re: [patch 1/5] mm: exclude reserved pages from dirtyable memory Date: Fri, 30 Sep 2011 15:53:14 +0200 Message-ID: <20110930135314.GA869@tiehlicka.suse.cz> References: <1317367044-475-1-git-send-email-jweiner@redhat.com> <1317367044-475-2-git-send-email-jweiner@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andrew Morton , Mel Gorman , Christoph Hellwig , Dave Chinner , Wu Fengguang , Jan Kara , Rik van Riel , Minchan Kim , Chris Mason , Theodore Ts'o , Andreas Dilger , Shaohua Li , xfs@oss.sgi.com, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Johannes Weiner Return-path: Content-Disposition: inline In-Reply-To: <1317367044-475-2-git-send-email-jweiner@redhat.com> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Fri 30-09-11 09:17:20, Johannes Weiner wrote: > The amount of dirtyable pages should not include the full number of > free pages: there is a number of reserved pages that the page > allocator and kswapd always try to keep free. > > The closer (reclaimable pages - dirty pages) is to the number of > reserved pages, the more likely it becomes for reclaim to run into > dirty pages: > > +----------+ --- > | anon | | > +----------+ | > | | | > | | -- dirty limit new -- flusher new > | file | | | > | | | | > | | -- dirty limit old -- flusher old > | | | > +----------+ --- reclaim > | reserved | > +----------+ > | kernel | > +----------+ > > This patch introduces a per-zone dirty reserve that takes both the > lowmem reserve as well as the high watermark of the zone into account, > and a global sum of those per-zone values that is subtracted from the > global amount of dirtyable pages. The lowmem reserve is unavailable > to page cache allocations and kswapd tries to keep the high watermark > free. We don't want to end up in a situation where reclaim has to > clean pages in order to balance zones. > > Not treating reserved pages as dirtyable on a global level is only a > conceptual fix. In reality, dirty pages are not distributed equally > across zones and reclaim runs into dirty pages on a regular basis. > > But it is important to get this right before tackling the problem on a > per-zone level, where the distance between reclaim and the dirty pages > is mostly much smaller in absolute numbers. > > Signed-off-by: Johannes Weiner > Reviewed-by: Rik van Riel Makes sense. Reviewed-by: Michal Hocko > --- > include/linux/mmzone.h | 6 ++++++ > include/linux/swap.h | 1 + > mm/page-writeback.c | 6 ++++-- > mm/page_alloc.c | 19 +++++++++++++++++++ > 4 files changed, 30 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 1ed4116..37a61e7 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -317,6 +317,12 @@ struct zone { > */ > unsigned long lowmem_reserve[MAX_NR_ZONES]; > > + /* > + * This is a per-zone reserve of pages that should not be > + * considered dirtyable memory. > + */ > + unsigned long dirty_balance_reserve; > + > #ifdef CONFIG_NUMA > int node; > /* > diff --git a/include/linux/swap.h b/include/linux/swap.h > index 3808f10..5e70f65 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -209,6 +209,7 @@ struct swap_list_t { > /* linux/mm/page_alloc.c */ > extern unsigned long totalram_pages; > extern unsigned long totalreserve_pages; > +extern unsigned long dirty_balance_reserve; > extern unsigned int nr_free_buffer_pages(void); > extern unsigned int nr_free_pagecache_pages(void); > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index da6d263..c8acf8a 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -170,7 +170,8 @@ static unsigned long highmem_dirtyable_memory(unsigned long total) > &NODE_DATA(node)->node_zones[ZONE_HIGHMEM]; > > x += zone_page_state(z, NR_FREE_PAGES) + > - zone_reclaimable_pages(z); > + zone_reclaimable_pages(z) - > + zone->dirty_balance_reserve; > } > /* > * Make sure that the number of highmem pages is never larger > @@ -194,7 +195,8 @@ static unsigned long determine_dirtyable_memory(void) > { > unsigned long x; > > - x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages(); > + x = global_page_state(NR_FREE_PAGES) + global_reclaimable_pages() - > + dirty_balance_reserve; > > if (!vm_highmem_is_dirtyable) > x -= highmem_dirtyable_memory(x); > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 1dba05e..f8cba89 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -96,6 +96,14 @@ EXPORT_SYMBOL(node_states); > > unsigned long totalram_pages __read_mostly; > unsigned long totalreserve_pages __read_mostly; > +/* > + * When calculating the number of globally allowed dirty pages, there > + * is a certain number of per-zone reserves that should not be > + * considered dirtyable memory. This is the sum of those reserves > + * over all existing zones that contribute dirtyable memory. > + */ > +unsigned long dirty_balance_reserve __read_mostly; > + > int percpu_pagelist_fraction; > gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK; > > @@ -5076,8 +5084,19 @@ static void calculate_totalreserve_pages(void) > if (max > zone->present_pages) > max = zone->present_pages; > reserve_pages += max; > + /* > + * Lowmem reserves are not available to > + * GFP_HIGHUSER page cache allocations and > + * kswapd tries to balance zones to their high > + * watermark. As a result, neither should be > + * regarded as dirtyable memory, to prevent a > + * situation where reclaim has to clean pages > + * in order to balance the zones. > + */ > + zone->dirty_balance_reserve = max; > } > } > + dirty_balance_reserve = reserve_pages; > totalreserve_pages = reserve_pages; > } > > -- > 1.7.6.2 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: email@kvack.org -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org