From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: blk_congestion_wait racy? Message-ID: From: Martin Schwidefsky Date: Mon, 8 Mar 2004 14:38:16 +0100 MIME-Version: 1.0 Content-type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: > Gad, that'll make the VM scan its guts out. Yes, I expected something like this. > > 2.6.4-rc2 + "fix" with 1 cpu > > sys 0m0.880s > > > > 2.6.4-rc2 + "fix" with 2 cpu > > sys 0m1.560s > > system time was doubled though. That would be the additional cost for not waiting. > Nope, something is obviously broken. I'll take a look. That would be very much appreciated. > Perhaps with two CPUs you are able to get kswapd and mempig running page > reclaim at the same time, which causes seekier swap I/O patterns than with > one CPU, where we only run one app or the other at any time. > > Serialising balance_pgdat() and try_to_free_pages() with a global semaphore > would be a way of testing that theory. Just tried the following patch: Index: mm/vmscan.c =================================================================== RCS file: /home/cvs/linux-2.5/mm/vmscan.c,v retrieving revision 1.45 diff -u -r1.45 vmscan.c --- mm/vmscan.c 18 Feb 2004 17:45:28 -0000 1.45 +++ mm/vmscan.c 8 Mar 2004 13:30:56 -0000 @@ -848,6 +848,7 @@ * excessive rotation of the inactive list, which is _supposed_ to be an LRU, * yes? */ +static DECLARE_MUTEX(reclaim_sem); int try_to_free_pages(struct zone **zones, unsigned int gfp_mask, unsigned int order) { @@ -858,6 +859,8 @@ struct reclaim_state *reclaim_state = current->reclaim_state; int i; + down(&reclaim_sem); + inc_page_state(allocstall); for (i = 0; zones[i] != 0; i++) @@ -884,7 +887,10 @@ wakeup_bdflush(total_scanned); /* Take a nap, wait for some writeback to complete */ + up(&reclaim_sem); blk_congestion_wait(WRITE, HZ/10); + down(&reclaim_sem); + if (zones[0] - zones[0]->zone_pgdat->node_zones < ZONE_HIGHMEM) { shrink_slab(total_scanned, gfp_mask); if (reclaim_state) { @@ -898,6 +904,9 @@ out: for (i = 0; zones[i] != 0; i++) zones[i]->prev_priority = zones[i]->temp_priority; + + up(&reclaim_sem); + return ret; } @@ -926,6 +935,8 @@ int i; struct reclaim_state *reclaim_state = current->reclaim_state; + down(&reclaim_sem); + inc_page_state(pageoutrun); for (i = 0; i < pgdat->nr_zones; i++) { @@ -974,8 +985,11 @@ } if (all_zones_ok) break; - if (to_free > 0) + if (to_free > 0) { + up(&reclaim_sem); blk_congestion_wait(WRITE, HZ/10); + down(&reclaim_sem); + } } for (i = 0; i < pgdat->nr_zones; i++) { @@ -983,6 +997,9 @@ zone->prev_priority = zone->temp_priority; } + + up(&reclaim_sem); + return nr_pages - to_free; } It didn't help. Still needs almost a minute. blue skies, Martin -- 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: aart@kvack.org