On Tue, Aug 24, 2010 at 01:14:16AM +0800, Minchan Kim wrote: > On Mon, Aug 23, 2010 at 07:23:16AM +0800, Wu Fengguang wrote: > > > From: Minchan Kim <minchan.kim@xxxxxxxxx> > > > Date: Mon, 23 Aug 2010 00:20:44 +0900 > > > Subject: [PATCH] compaction: handle active and inactive fairly in too_many_isolated > > > > > > Iram reported compaction's too_many_isolated loops forever. > > > (http://www.spinics.net/lists/linux-mm/msg08123.html) > > > > > > The meminfo of situation happened was inactive anon is zero. > > > That's because the system has no memory pressure until then. > > > While all anon pages was in active lru, compaction could select > > > active lru as well as inactive lru. That's different things > > > with vmscan's isolated. So we has been two too_many_isolated. > > > > > > While compaction can isolated pages in both active and inactive, > > > current implementation of too_many_isolated only considers inactive. > > > It made Iram's problem. > > > > > > This patch handles active and inactie with fair. > > > That's because we can't expect where from and how many compaction would > > > isolated pages. > > > > > > This patch changes (nr_isolated > nr_inactive) with > > > nr_isolated > (nr_active + nr_inactive) / 2. > > > > The change looks good, thanks. However I'm not sure if it's enough. > > > > I wonder where the >40MB isolated pages come about. inactive_anon > > remains 0 and free remains high over a long time, so it seems there > > are no concurrent direct reclaims at all. Are the pages isolated by > > the compaction process itself? > > I think it can't happen without kswapd or direct reclaim. > But I think direct reclaim doesn't happen becuase Iram has no activity on system > at that time. So just geussing following scenario. > > 1. trigger compaction by proc > 2. isolate some pages and then migrate_pages > 3. migrate_pages calls cond_resched > 4. someone need big page(I am not sure this part) > 4. kswapd: shrink anon active list due to inactive_anon_is_low > 5. kswapd: isolate_lru_pages for order > 0 (ex, 0.5M page) so 0.5 M * 32 = 16M are isolated > 6. kswapd: shrink_zone : shrink anon active list due to inactive_anon_is_low > 7. kswapd: isolate_lru_pages for order > 0 (ex, 0.5M page) so 0.5 M * 32 are isolated again. > > Does it make sense? One question is, why kswapd won't proceed after isolating all the pages? If it has done with the isolated pages, we'll see growing inactive_anon numbers. /proc/vmstat should give more clues on any possible page reclaim activities. Iram, would you help post it? Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>