On Wed, Aug 31, 2022 at 11:02:49AM +0100, Mel Gorman wrote: > On Tue, Aug 30, 2022 at 02:48:52PM -0700, Suren Baghdasaryan wrote: > > From: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > > > This patch adds lib/lazy-percpu-counter.c, which implements counters > > that start out as atomics, but lazily switch to percpu mode if the > > update rate crosses some threshold (arbitrarily set at 256 per second). > > > > Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > Why not use percpu_counter? It has a per-cpu counter that is synchronised > when a batch threshold (default 32) is exceeded and can explicitly sync > the counters when required assuming the synchronised count is only needed > when reading debugfs. It doesn't switch from atomic mode to percpu mode when the update rate crosses a threshold like lazy percpu counters does, it allocates all the percpu counters up front - that makes it a non starter here. Also, from my reading of the code... wtf is it even doing, and why would I use it at all? This looks like old grotty code from ext3, it's not even using this_cpu_add() - it does preempt_enable()/disable() just for adding to a local percpu counter! Noooooope.
