Hello, Johannes. Just nitpick below. On Mon, Feb 22, 2016 at 03:33:22PM -0800, Johannes Weiner wrote: > In machines with 140G of memory and enterprise flash storage, we have > seen read and write bursts routinely exceed the kswapd watermarks and > cause thundering herds in direct reclaim. Unfortunately, the only way > to tune kswapd aggressiveness is through adjusting min_free_kbytes - > the system's emergency reserves - which is entirely unrelated to the > system's latency requirements. In order to get kswapd to maintain a > 250M buffer of free memory, the emergency reserves need to be set to > 1G. That is a lot of memory wasted for no good reason. > > On the other hand, it's reasonable to assume that allocation bursts > and overall allocation concurrency scale with memory capacity, so it > makes sense to make kswapd aggressiveness a function of that as well. > > Change the kswapd watermark scale factor from the currently fixed 25% > of the tunable emergency reserve to a tunable 0.001% of memory. s/0.001%/0.1% > Beyond 1G of memory, this will produce bigger watermark steps than the > current formula in default settings. Ensure that the new formula never > chooses steps smaller than that, i.e. 25% of the emergency reserve. > > On a 140G machine, this raises the default watermark steps - the > distance between min and low, and low and high - from 16M to 143M. > > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> > Acked-by: Mel Gorman <mgorman@xxxxxxx> > --- > Documentation/sysctl/vm.txt | 18 ++++++++++++++++++ > include/linux/mm.h | 1 + > include/linux/mmzone.h | 2 ++ > kernel/sysctl.c | 10 ++++++++++ > mm/page_alloc.c | 29 +++++++++++++++++++++++++++-- > 5 files changed, 58 insertions(+), 2 deletions(-) > > v2: Ensure 25% of emergency reserves as a minimum on small machines -Rik > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > index 89a887c..b02d940 100644 > --- a/Documentation/sysctl/vm.txt > +++ b/Documentation/sysctl/vm.txt > @@ -803,6 +803,24 @@ performance impact. Reclaim code needs to take various locks to find freeable > directory and inode objects. With vfs_cache_pressure=1000, it will look for > ten times more freeable objects than there are. > > +============================================================= > + > +watermark_scale_factor: > + > +This factor controls the aggressiveness of kswapd. It defines the > +amount of memory left in a node/system before kswapd is woken up and > +how much memory needs to be free before kswapd goes back to sleep. > + > +The unit is in fractions of 10,000. The default value of 10 means the > +distances between watermarks are 0.001% of the available memory in the > +node/system. The maximum value is 1000, or 10% of memory. Ditto for 0.001%. Thanks. -- 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>