On Mon, 2012-12-10 at 10:48 +0800, Fengguang Wu wrote: > Neil find that if too_many_isolated() returns true while performing > direct reclaim we can end up waiting for other threads to complete their > direct reclaim. If those threads are allowed to enter the FS or IO to > free memory, but this thread is not, then it is possible that those > threads will be waiting on this thread and so we get a circular > deadlock. > > some task enters direct reclaim with GFP_KERNEL > => too_many_isolated() false > => vmscan and run into dirty pages > => pageout() > => take some FS lock > => fs/block code does GFP_NOIO allocation Hi Fengguang, GFP_NOIO allocation for what? > => enter direct reclaim again > => too_many_isolated() true > => waiting for others to progress, however the other > tasks may be circular waiting for the FS lock.. > > The fix is to let !__GFP_IO and !__GFP_FS direct reclaims enjoy higher > priority than normal ones, by lowering the throttle threshold for the > latter. > > Allowing ~1/8 isolated pages in normal is large enough. For example, > for a 1GB LRU list, that's ~128MB isolated pages, or 1k blocked tasks > (each isolates 32 4KB pages), or 64 blocked tasks per logical CPU > (assuming 16 logical CPUs per NUMA node). So it's not likely some CPU > goes idle waiting (when it could make progress) because of this limit: > there are much more sleeping reclaim tasks than the number of CPU, so > the task may well be blocked by some low level queue/lock anyway. > > Now !GFP_IOFS reclaims won't be waiting for GFP_IOFS reclaims to > progress. They will be blocked only when there are too many concurrent > !GFP_IOFS reclaims, however that's very unlikely because the IO-less Why you said that direct reclaim is IO-less? > direct reclaims is able to progress much more faster, and they won't > deadlock each other. The threshold is raised high enough for them, so > that there can be sufficient parallel progress of !GFP_IOFS reclaims. > > CC: Torsten Kaiser <just.for.lkml@xxxxxxxxxxxxxx> > Tested-by: NeilBrown <neilb@xxxxxxx> > Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx> > Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Acked-by: Rik van Riel <riel@xxxxxxxxxx> > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> > --- > mm/vmscan.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > --- linux-next.orig/mm/vmscan.c 2012-12-10 10:43:06.474928860 +0800 > +++ linux-next/mm/vmscan.c 2012-12-10 10:43:09.022928920 +0800 > @@ -1202,6 +1202,13 @@ static int too_many_isolated(struct zone > isolated = zone_page_state(zone, NR_ISOLATED_ANON); > } > > + /* > + * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so that > + * they won't get blocked by normal ones and form circular deadlock. > + */ > + if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS) > + inactive >>= 3; > + > return isolated > inactive; > } > > > -- > 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/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>