Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754249Ab0K3WZo (ORCPT ); Tue, 30 Nov 2010 17:25:44 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:52081 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752549Ab0K3WZn (ORCPT ); Tue, 30 Nov 2010 17:25:43 -0500 Date: Tue, 30 Nov 2010 14:25:09 -0800 From: Andrew Morton To: Balbir Singh Cc: linux-mm@kvack.org, Christoph Lameter , linux-kernel@vger.kernel.org, kvm Subject: Re: [PATCH 3/3] Provide control over unmapped pages Message-Id: <20101130142509.4f49d452.akpm@linux-foundation.org> In-Reply-To: <20101130101602.17475.32611.stgit@localhost6.localdomain6> References: <20101130101126.17475.18729.stgit@localhost6.localdomain6> <20101130101602.17475.32611.stgit@localhost6.localdomain6> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; 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: 6690 Lines: 195 On Tue, 30 Nov 2010 15:46:31 +0530 Balbir Singh wrote: > Provide control using zone_reclaim() and a boot parameter. The > code reuses functionality from zone_reclaim() to isolate unmapped > pages and reclaim them as a priority, ahead of other mapped pages. > > Signed-off-by: Balbir Singh > --- > include/linux/swap.h | 5 ++- > mm/page_alloc.c | 7 +++-- > mm/vmscan.c | 72 +++++++++++++++++++++++++++++++++++++++++++++++++- > 3 files changed, 79 insertions(+), 5 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index eba53e7..78b0830 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -252,11 +252,12 @@ extern int vm_swappiness; > extern int remove_mapping(struct address_space *mapping, struct page *page); > extern long vm_total_pages; > > -#ifdef CONFIG_NUMA > -extern int zone_reclaim_mode; > extern int sysctl_min_unmapped_ratio; > extern int sysctl_min_slab_ratio; This change will need to be moved into the first patch. > extern int zone_reclaim(struct zone *, gfp_t, unsigned int); > +extern bool should_balance_unmapped_pages(struct zone *zone); > +#ifdef CONFIG_NUMA > +extern int zone_reclaim_mode; > #else > #define zone_reclaim_mode 0 > static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order) > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 62b7280..4228da3 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1662,6 +1662,9 @@ zonelist_scan: > unsigned long mark; > int ret; > > + if (should_balance_unmapped_pages(zone)) > + wakeup_kswapd(zone, order); gack, this is on the page allocator fastpath, isn't it? So 99.99999999% of the world's machines end up doing a pointless call to a pointless function which pointlessly tests a pointless global and pointlessly returns? All because of some whacky KSM thing? The speed and space overhead of this code should be *zero* if !CONFIG_UNMAPPED_PAGECACHE_CONTROL and should be minimal if CONFIG_UNMAPPED_PAGECACHE_CONTROL=y. The way to do the latter is to inline the test of unmapped_page_control into callers and only if it is true (and use unlikely(), please) do we call into the KSM gunk. > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -145,6 +145,21 @@ static DECLARE_RWSEM(shrinker_rwsem); > #define scanning_global_lru(sc) (1) > #endif > > +static unsigned long balance_unmapped_pages(int priority, struct zone *zone, > + struct scan_control *sc); > +static int unmapped_page_control __read_mostly; > + > +static int __init unmapped_page_control_parm(char *str) > +{ > + unmapped_page_control = 1; > + /* > + * XXX: Should we tweak swappiness here? > + */ > + return 1; > +} > +__setup("unmapped_page_control", unmapped_page_control_parm); aw c'mon guys, everybody knows that when you add a kernel parameter you document it in Documentation/kernel-parameters.txt. > static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone, > struct scan_control *sc) > { > @@ -2223,6 +2238,12 @@ loop_again: > shrink_active_list(SWAP_CLUSTER_MAX, zone, > &sc, priority, 0); > > + /* > + * We do unmapped page balancing once here and once > + * below, so that we don't lose out > + */ > + balance_unmapped_pages(priority, zone, &sc); > + > if (!zone_watermark_ok_safe(zone, order, > high_wmark_pages(zone), 0, 0)) { > end_zone = i; > @@ -2258,6 +2279,11 @@ loop_again: > continue; > > sc.nr_scanned = 0; > + /* > + * Balance unmapped pages upfront, this should be > + * really cheap > + */ > + balance_unmapped_pages(priority, zone, &sc); More unjustifiable overhead on a commonly-executed codepath. > /* > * Call soft limit reclaim before calling shrink_zone. > @@ -2491,7 +2517,8 @@ void wakeup_kswapd(struct zone *zone, int order) > pgdat->kswapd_max_order = order; > if (!waitqueue_active(&pgdat->kswapd_wait)) > return; > - if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) > + if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0) && > + !should_balance_unmapped_pages(zone)) > return; > > trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); > @@ -2740,6 +2767,49 @@ zone_reclaim_unmapped_pages(struct zone *zone, struct scan_control *sc, > } > > /* > + * Routine to balance unmapped pages, inspired from the code under > + * CONFIG_NUMA that does unmapped page and slab page control by keeping > + * min_unmapped_pages in the zone. We currently reclaim just unmapped > + * pages, slab control will come in soon, at which point this routine > + * should be called balance cached pages > + */ The problem I have with this comment is that it uses the term "balance" without ever defining it. Plus "balance" is already a term which is used in memory reclaim. So if you can think up a unique noun then that's good but whether or not that is done, please describe with great care what that term actually means in this context. > +static unsigned long balance_unmapped_pages(int priority, struct zone *zone, > + struct scan_control *sc) > +{ > + if (unmapped_page_control && > + (zone_unmapped_file_pages(zone) > zone->min_unmapped_pages)) { > + struct scan_control nsc; > + unsigned long nr_pages; > + > + nsc = *sc; > + > + nsc.swappiness = 0; > + nsc.may_writepage = 0; > + nsc.may_unmap = 0; > + nsc.nr_reclaimed = 0; Doing a clone-and-own of a scan_control is novel. What's going on here? > + nr_pages = zone_unmapped_file_pages(zone) - > + zone->min_unmapped_pages; > + /* Magically try to reclaim eighth the unmapped cache pages */ > + nr_pages >>= 3; > + > + zone_reclaim_unmapped_pages(zone, &nsc, nr_pages); > + return nsc.nr_reclaimed; > + } > + return 0; > +} > + > +#define UNMAPPED_PAGE_RATIO 16 Well. Giving 16 a name didn't really clarify anything. Attentive readers will want to know what this does, why 16 was chosen and what the effects of changing it will be. > +bool should_balance_unmapped_pages(struct zone *zone) > +{ > + if (unmapped_page_control && > + (zone_unmapped_file_pages(zone) > > + UNMAPPED_PAGE_RATIO * zone->min_unmapped_pages)) > + return true; > + return false; > +} > Reviewed-by: Christoph Lameter So you're OK with shoving all this flotsam into 100,000,000 cellphones? This was a pretty outrageous patchset! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/