On Wed, Aug 22, 2012 at 04:00:25PM +1000, NeilBrown wrote: > On Wed, 22 Aug 2012 11:57:02 +0800 Yuanhan Liu <yuanhan.liu@xxxxxxxxxxxxxxx> > wrote: > > > > > -#define NR_STRIPES 256 > > +#define NR_STRIPES 1024 > > Changing one magic number into another magic number might help your case, but > it not really a general solution. Agreed. > > Possibly making sure that max_nr_stripes is at least some multiple of the > chunk size might make sense, but I wouldn't want to see a very large multiple. > > I thing the problems with RAID5 are deeper than that. Hopefully I'll figure > out exactly what the best fix is soon - I'm trying to look into it. > > I don't think the size of the cache is a big part of the solution. I think > correct scheduling of IO is the real answer. Yes, it should not be. But with less max_nr_stripes, the chance to get a full strip write is less, and maybe that's the reason why the chance to block at get_active_strip() is more; and also, the reading is more. The perfect case would be there are no reading; setting max_nr_stripes to 32768(the max we get set now), you will find the reading is quite less(almost zero, please see the iostat I attached in former email). Anyway, I do agree this should not be the big part of the solution. If we can handle those stripes faster, I guess 256 would be enough. Thanks, Yuanhan Liu -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
