Christoph Hellwig <hch@xxxxxxxxxxxxx> writes: > On Wed, Sep 03, 2014 at 10:01:58AM +1000, NeilBrown wrote: >> Do we still need maximums at all? > > I don't think we do. At least on any system I work with I have to > increase them to get good performance without any adverse effect on > throttling. > >> So can we just remove the limit on max_sectors and the RAID5 stripe cache >> size? I'm certainly keen to remove the later and just use a mempool if the >> limit isn't needed. >> I have seen reports that a very large raid5 stripe cache size can cause >> a reduction in performance. I don't know why but I suspect it is a bug that >> should be found and fixed. >> >> Do we need max_sectors ?? I'm assuming we're talking about max_sectors_kb in /sys/block/sdX/queue/. > I'll send a patch to remove it and watch for the fireworks.. :) I've seen SSDs that actually degrade in performance if I/O sizes exceed their internal page size (using artificial benchmarks; I never confirmed that with actual workloads). Bumping the default might not be bad, but getting rid of the tunable would be a step backwards, in my opinion. Are you going to bump up BIO_MAX_PAGES while you're at it? Cheers, Jeff -- 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>