From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 26 Jul 2005 18:26:31 -0700 From: Andrew Morton Subject: Re: Memory pressure handling with iSCSI Message-Id: <20050726182631.668e2da2.akpm@osdl.org> In-Reply-To: <194200000.1122427210@flay> References: <1122399331.6433.29.camel@dyn9047017102.beaverton.ibm.com> <20050726111110.6b9db241.akpm@osdl.org> <1122403152.6433.39.camel@dyn9047017102.beaverton.ibm.com> <20050726114824.136d3dad.akpm@osdl.org> <20050726121250.0ba7d744.akpm@osdl.org> <1122412301.6433.54.camel@dyn9047017102.beaverton.ibm.com> <20050726142410.4ff2e56a.akpm@osdl.org> <1122414300.6433.57.camel@dyn9047017102.beaverton.ibm.com> <20050726151003.6aa3aecb.akpm@osdl.org> <1122418089.6433.62.camel@dyn9047017102.beaverton.ibm.com> <20050726160728.55245dae.akpm@osdl.org> <1122420376.6433.68.camel@dyn9047017102.beaverton.ibm.com> <20050726173126.5368266b.akpm@osdl.org> <194200000.1122427210@flay> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Martin J. Bligh" Cc: pbadari@us.ibm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: "Martin J. Bligh" wrote: > > > > It happens here, a bit. My machine goes up to 60% dirty when it should be > > clamping at 40%. > > > > The variable `total_pages' in page-writeback.c (from > > nr_free_pagecache_pages()) is too high. I trace it back to here: > > > > On node 0 totalpages: 1572864 > > DMA zone: 4096 pages, LIFO batch:1 > > Normal zone: 1568768 pages, LIFO batch:31 > > HighMem zone: 0 pages, LIFO batch:1 > > > > This machine only has 4G of memory, so the platform code is overestimating > > the number of pages by 50%. Can you please check your dmesg, see if your > > system is also getting this wrong? > > I think we're repeatedly iterating over the same zones by walking the > zonelists: > > static unsigned int nr_free_zone_pages(int offset) > { > pg_data_t *pgdat; > unsigned int sum = 0; > int i; > > for_each_pgdat(pgdat) { > struct zone *zone; > > for (i = 0; i < MAX_NR_ZONES; i++) { > unsigned long size, high; > > zone = pgdat->node_zones[i]; > size = zone->present_pages; > high = zone->pages_high; > > if (size > high) > sum += size - high; > } > } > } I don't think so. We're getting the wrong answer out of calculate_zone_totalpages() which is an init-time thing. Maybe nr_free_zone_pages() is supposed to fix that up post-facto somehow, but calculate_zone_totalpages() sure as heck shouldn't be putting 1568768 into my ZONE_NORMAL's ->node_present_pages. -- 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: email@kvack.org