On Wed, Nov 05, 2014 at 09:38, David Gwynne wrote: > >> On 30 Oct 2014, at 07:52, Ted Unangst <t...@tedunangst.com> wrote: >> >> On Wed, Oct 29, 2014 at 07:25, David Gwynne wrote: >> >> >>> i dunno. im fine with either removing colouring altogether or setting it >>> from something else completely. i just want a decision to be made cos >>> right now ph_color isnt set, which is a bug. >> >> there. i fixed it. > > looks like we were both ignorant and wrong. mikeb@ points out this from > the original slab paper: > > 4.1. Impact of Buffer Address Distribution on Cache > Utilization > > The address distribution of mid-size buffers can > affect the system’s overall cache utilization. In par- > ticular, power-of-two allocators - where all buffers > are 2 n bytes and are 2 n -byte aligned - are pes- > simal.* Suppose, for example, that every inode > (∼ 300 bytes) is assigned a 512-byte buffer, 512-byte > aligned, and that only the first dozen fields of an > inode (48 bytes) are frequently referenced. Then > the majority of inode-related memory traffic will be > at addresses between 0 and 47 modulo 512. Thus > the cache lines near 512-byte boundaries will be > heavily loaded while the rest lie fallow. In effect > only 9% (48/512) of the cache will be usable by > inodes. Fully-associative caches would not suffer > this problem, but current hardware trends are toward > simpler rather than more complex caches.
except pool won't align a 300 byte inode on 512 byte boundaries.
