On Thu, Mar 11, 2021 at 08:54:12PM +0900, Namhyung Kim wrote: > From: Namhyung Kim <namhy...@google.com> > > The kernel can allocate a lot of struct perf_event when profiling. For > example, 256 cpu x 8 events x 20 cgroups = 40K instances of the struct > would be allocated on a large system. > > The size of struct perf_event in my setup is 1152 byte. As it's > allocated by kmalloc, the actual allocation size would be rounded up > to 2K. > > Then there's 896 byte (~43%) of waste per instance resulting in total > ~35MB with 40K instances. We can create a dedicated kmem_cache to > avoid such a big unnecessary memory consumption. > > With this change, I can see below (note this machine has 112 cpus). > > # grep perf_event /proc/slabinfo > perf_event 224 784 1152 7 2 : tunables 24 12 8 : > slabdata 112 112 0 > > The sixth column is pages-per-slab which is 2, and the fifth column is > obj-per-slab which is 7. Thus actually it can use 1152 x 7 = 8064 > byte in the 8K, and wasted memory is (8192 - 8064) / 7 = ~18 byte per > instance. > > Signed-off-by: Namhyung Kim <namhy...@kernel.org>
Thanks for both!
