On Thu, 2 Mar 2017 00:33:45 -0500 Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote: > Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT > is provided every time memory quadruples the sizes of hash tables will only > double instead of quadrupling as well. This algorithm starts working only > when memory size reaches a certain point, currently set to 64G. > > This is example of dentry hash table size, before and after four various > memory configurations: > > MEMORY SCALE HASH_SIZE > old new old new > 8G 13 13 8M 8M > 16G 13 13 16M 16M > 32G 13 13 32M 32M > 64G 13 13 64M 64M > 128G 13 14 128M 64M > 256G 13 14 256M 128M > 512G 13 15 512M 128M > 1024G 13 15 1024M 256M > 2048G 13 16 2048M 256M > 4096G 13 16 4096M 512M > 8192G 13 17 8192M 512M > 16384G 13 17 16384M 1024M > 32768G 13 18 32768M 1024M > 65536G 13 18 65536M 2048M OK, but what are the runtime effects? Presumably some workloads will slow down a bit. How much? How do we know that this is a worthwhile tradeoff? If the effect of this change is "undetectable" then those hash tables are simply too large, and additional tuning is needed, yes?
