On Fri 13-07-18 10:36:14, Dave Chinner wrote: [...] > By limiting the number of negative dentries in this case, internal > slab fragmentation is reduced such that reclaim cost never gets out > of control. While it appears to "fix" the symptoms, it doesn't > address the underlying problem. It is a partial solution at best but > at worst it's another opaque knob that nobody knows how or when to > tune. Would it help to put all the negative dentries into its own slab cache? > Very few microbenchmarks expose this internal slab fragmentation > problem because they either don't run long enough, don't create > memory pressure, or don't have access patterns that mix long and > short term slab objects together in a way that causes slab > fragmentation. Run some cold cache directory traversals (git > status?) at the same time you are creating negative dentries so you > create pinned partial pages in the slab cache and see how the > behaviour changes.... Agreed! Slab fragmentation is a real problem we are seeing for quite some time. We should try to address it rather than paper over it with weird knobs. -- Michal Hocko SUSE Labs
