On Tue, 27 Dec 2011 12:57:31 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote: > On Tue, Dec 27, 2011 at 11:15:43AM +0900, KAMEZAWA Hiroyuki wrote: > > On Sat, 24 Dec 2011 07:45:03 +1100 > > Dave Chinner <david@xxxxxxxxxxxxx> wrote: > > > > > On Fri, Dec 23, 2011 at 03:04:02PM +0400, nowhere wrote: > > > > В Пт., 23/12/2011 в 21:20 +1100, Dave Chinner пишет: > > > > > On Fri, Dec 23, 2011 at 01:01:20PM +0400, nowhere wrote: > > > > > > В Чт., 22/12/2011 в 09:55 +1100, Dave Chinner пишет: > > > > > > > On Wed, Dec 21, 2011 at 10:52:49AM +0100, Michal Hocko wrote: > > > > > > Here is the report of trace-cmd while dd'ing > > > > https://80.237.6.56/report-dd.xz > > > > > > Ok, it's not a shrink_slab() problem - it's just being called ~100uS > > > by kswapd. The pattern is: > > > > > > - reclaim 94 (batches of 32,32,30) pages from iinactive list > > > of zone 1, node 0, prio 12 > > > - call shrink_slab > > > - scan all caches > > > - all shrinkers return 0 saying nothing to shrink > > > - 40us gap > > > - reclaim 10-30 pages from inactive list of zone 2, node 0, prio 12 > > > - call shrink_slab > > > - scan all caches > > > - all shrinkers return 0 saying nothing to shrink > > > - 40us gap > > > - isolate 9 pages from LRU zone ?, node ?, none isolated, none freed > > > - isolate 22 pages from LRU zone ?, node ?, none isolated, none freed > > > - call shrink_slab > > > - scan all caches > > > - all shrinkers return 0 saying nothing to shrink > > > 40us gap > > > > > > And it just repeats over and over again. After a while, nid=0,zone=1 > > > drops out of the traces, so reclaim only comes in batches of 10-30 > > > pages from zone 2 between each shrink_slab() call. > > > > > > The trace starts at 111209.881s, with 944776 pages on the LRUs. It > > > finishes at 111216.1 with kswapd going to sleep on node 0 with > > > 930067 pages on the LRU. So 7 seconds to free 15,000 pages (call it > > > 2,000 pages/s) which is awfully slow.... > > > > > > vmscan gurus - time for you to step in now... > > > > > > > Can you show /proc/zoneinfo ? I want to know each zone's size. > > > > Below is my memo. > > > > In trace log, priority = 11 or 12. Then, I think kswapd can reclaim memory > > to satisfy "sc.nr_reclaimed >= SWAP_CLUSTER_MAX" condition and loops again. > > > > Seeing balance_pgdat() and trace log, I guess it does > > > > wake up > > > > shrink_zone(zone=0(DMA?)) => nothing to reclaim. > > shrink_slab() > > shrink_zone(zone=1(DMA32?)) => reclaim 32,32,31 pages > > shrink_slab() > > shrink_zone(zone=2(NORMAL?)) => reclaim 13 pages. > > srhink_slab() > > > > sleep or retry. > > > > Why shrink_slab() need to be called frequently like this ? > > I guess it's caused by small NORMAL zone. You're right. I confirmed his zoneinfo. > The scenario I think is as follows, > > 1. dd comsumes memory in NORMAL zone > 2. dd enter direct reclaim and wakeup kswapd > 3. kswapd reclaims some memory in NORMAL zone until it reclaims high wamrk > 4. schedule > 5. dd consumes memory again in NORMAL zone > 6. kswapd fail to reclaim memory by high watermark due to 5. > 7. loop again, goto 3. > > The point is speed between reclaim VS memory consumption. > So kswapd cannot reach a point which enough pages are in NORMAL zone. > > > > > BTW. I'm sorry if I miss something ...Why only kswapd reclaims memory > > while 'dd' operation ? (no direct relcaim by dd.) > > Is this log record cpu hog after 'dd' ? > > If above scenario is right, dd couldn't enter direct reclaim to reclaim memory. > I think you're right. IIUC, kswapd's behavior is what we usually see. Hmm, if I understand correctly, - dd's speed down is caused by kswapd's cpu consumption. - kswapd's cpu consumption is enlarged by shrink_slab() (by perf) - kswapd can't stop because NORMAL zone is small. - memory reclaim speed is enough because dd can't get enough cpu. I wonder reducing to call shrink_slab() may be a help but I'm not sure where lock conention comes from... Regards, -Kame -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>