From: Mel Gorman <mel@csn.ul.ie> To: Andrew Morton <akpm@linux-foundation.org> Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Linux Kernel List <linux-kernel@vger.kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Minchan Kim <minchan.kim@gmail.com>, Wu Fengguang <fengguang.wu@intel.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Subject: Re: [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone Date: Tue, 21 Sep 2010 23:10:08 +0100 [thread overview] Message-ID: <20100921221008.GA16323@csn.ul.ie> (raw) In-Reply-To: <20100921144413.abc45d2f.akpm@linux-foundation.org> On Tue, Sep 21, 2010 at 02:44:13PM -0700, Andrew Morton wrote: > On Mon, 20 Sep 2010 10:52:39 +0100 > Mel Gorman <mel@csn.ul.ie> wrote: > > > > > This patch tracks how many pages backed by a congested BDI were found during > > > > scanning. If all the dirty pages encountered on a list isolated from the > > > > LRU belong to a congested BDI, the zone is marked congested until the zone > > > > reaches the high watermark. > > > > > > High watermark, or low watermark? > > > > > > > High watermark. The check is made by kswapd. > > > > > The terms are rather ambiguous so let's avoid them. Maybe "full" > > > watermark and "empty"? > > > > > > > Unfortunately they are ambiguous to me. I know what the high watermark > > is but not what the full or empty watermarks are. > > Really. So what's the "high" watermark? The high watermark is the point where kswapd goes back to sleep because enough pages have been reclaimed. It's a proxy measure for memory pressure. > From the above text I'm > thinking that you mean the high watermark is when the queue has a small > number of requests and the low watermark is when the queue has a large > number of requests. > I was expecting "zone reaches the high watermark" was the clue that I was talking about zone watermarks and not an IO queue but it could be better. > I'd have thought that this is backwards: the "high" watermark is when > the queue has a large (ie: high) number of requests. > > A problem. How do we fix it? > I will try and clarify. How about this as a replacement paragraph? ==== CUT HERE ==== This patch tracks how many pages backed by a congested BDI were found during scanning. If all the dirty pages isolated from the LRU are backed by a congested BDI, the zone is marked congested. A zone is marked uncongested with enough pages have been freed for the zone's high watermark to be reached indicating that the zone is no longer under any memory pressure. wait_iff_congested() checks if there are any congested BDIs and if so if the current zone is marked congested. If both conditions are met, the caller sleeps on the congestion queue. Otherwise it will call cond_reched() to yield the processor if necessary. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab
WARNING: multiple messages have this Message-ID (diff)
From: Mel Gorman <mel@csn.ul.ie> To: Andrew Morton <akpm@linux-foundation.org> Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Linux Kernel List <linux-kernel@vger.kernel.org>, Johannes Weiner <hannes@cmpxchg.org>, Minchan Kim <minchan.kim@gmail.com>, Wu Fengguang <fengguang.wu@intel.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Subject: Re: [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone Date: Tue, 21 Sep 2010 23:10:08 +0100 [thread overview] Message-ID: <20100921221008.GA16323@csn.ul.ie> (raw) In-Reply-To: <20100921144413.abc45d2f.akpm@linux-foundation.org> On Tue, Sep 21, 2010 at 02:44:13PM -0700, Andrew Morton wrote: > On Mon, 20 Sep 2010 10:52:39 +0100 > Mel Gorman <mel@csn.ul.ie> wrote: > > > > > This patch tracks how many pages backed by a congested BDI were found during > > > > scanning. If all the dirty pages encountered on a list isolated from the > > > > LRU belong to a congested BDI, the zone is marked congested until the zone > > > > reaches the high watermark. > > > > > > High watermark, or low watermark? > > > > > > > High watermark. The check is made by kswapd. > > > > > The terms are rather ambiguous so let's avoid them. Maybe "full" > > > watermark and "empty"? > > > > > > > Unfortunately they are ambiguous to me. I know what the high watermark > > is but not what the full or empty watermarks are. > > Really. So what's the "high" watermark? The high watermark is the point where kswapd goes back to sleep because enough pages have been reclaimed. It's a proxy measure for memory pressure. > From the above text I'm > thinking that you mean the high watermark is when the queue has a small > number of requests and the low watermark is when the queue has a large > number of requests. > I was expecting "zone reaches the high watermark" was the clue that I was talking about zone watermarks and not an IO queue but it could be better. > I'd have thought that this is backwards: the "high" watermark is when > the queue has a large (ie: high) number of requests. > > A problem. How do we fix it? > I will try and clarify. How about this as a replacement paragraph? ==== CUT HERE ==== This patch tracks how many pages backed by a congested BDI were found during scanning. If all the dirty pages isolated from the LRU are backed by a congested BDI, the zone is marked congested. A zone is marked uncongested with enough pages have been freed for the zone's high watermark to be reached indicating that the zone is no longer under any memory pressure. wait_iff_congested() checks if there are any congested BDIs and if so if the current zone is marked congested. If both conditions are met, the caller sleeps on the congestion queue. Otherwise it will call cond_reched() to yield the processor if necessary. -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2010-09-21 22:10 UTC|newest] Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-09-15 12:27 [PATCH 0/8] Reduce latencies and improve overall reclaim efficiency v2 Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 1/8] tracing, vmscan: Add trace events for LRU list shrinking Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 2/8] writeback: Account for time spent congestion_waited Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 3/8] vmscan: Synchronous lumpy reclaim should not call congestion_wait() Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 4/8] vmscan: Narrow the scenarios lumpy reclaim uses synchrounous reclaim Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 5/8] vmscan: Remove dead code in shrink_inactive_list() Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 6/8] vmscan: isolated_lru_pages() stop neighbour search if neighbour cannot be isolated Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 7/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-16 7:59 ` Minchan Kim 2010-09-16 7:59 ` Minchan Kim 2010-09-16 8:23 ` Mel Gorman 2010-09-16 8:23 ` Mel Gorman 2010-09-15 12:27 ` [PATCH 8/8] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encountered in the current zone Mel Gorman 2010-09-15 12:27 ` Mel Gorman 2010-09-16 8:13 ` Minchan Kim 2010-09-16 8:13 ` Minchan Kim 2010-09-16 9:18 ` Mel Gorman 2010-09-16 9:18 ` Mel Gorman 2010-09-16 14:11 ` Minchan Kim 2010-09-16 14:11 ` Minchan Kim 2010-09-16 15:18 ` Mel Gorman 2010-09-16 15:18 ` Mel Gorman 2010-09-16 22:28 ` Andrew Morton 2010-09-16 22:28 ` Andrew Morton 2010-09-20 9:52 ` Mel Gorman 2010-09-20 9:52 ` Mel Gorman 2010-09-21 21:44 ` Andrew Morton 2010-09-21 21:44 ` Andrew Morton 2010-09-21 22:10 ` Mel Gorman [this message] 2010-09-21 22:10 ` Mel Gorman 2010-09-21 22:24 ` Andrew Morton 2010-09-21 22:24 ` Andrew Morton 2010-09-20 13:05 ` [PATCH] writeback: Do not sleep on the congestion queue if there are no congested BDIs or if significant congestion is not being encounted in the current zone fix Mel Gorman 2010-09-20 13:05 ` Mel Gorman 2010-09-16 22:28 ` [PATCH 0/8] Reduce latencies and improve overall reclaim efficiency v2 Andrew Morton 2010-09-16 22:28 ` Andrew Morton 2010-09-17 7:52 ` Mel Gorman 2010-09-17 7:52 ` Mel Gorman 2010-10-14 15:28 ` Christian Ehrhardt 2010-10-14 15:28 ` Christian Ehrhardt 2010-10-14 15:28 ` Christian Ehrhardt 2010-10-18 13:55 ` Mel Gorman 2010-10-18 13:55 ` Mel Gorman 2010-10-22 12:29 ` Christian Ehrhardt 2010-10-22 12:29 ` Christian Ehrhardt 2010-10-22 12:29 ` Christian Ehrhardt 2010-11-03 10:50 ` Christian Ehrhardt 2010-11-03 10:50 ` Christian Ehrhardt 2010-11-03 10:50 ` Christian Ehrhardt 2010-11-10 14:37 ` Mel Gorman 2010-11-10 14:37 ` Mel Gorman
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