On Wed 18-12-13 10:18:46, Johannes Weiner wrote: > On Wed, Dec 18, 2013 at 03:51:11PM +0100, Michal Hocko wrote: > > On Tue 17-12-13 15:02:10, Johannes Weiner wrote: > > [...] > > > +pagecache_mempolicy_mode: > > > + > > > +This is available only on NUMA kernels. > > > + > > > +Per default, the configured memory policy is applicable to anonymous > > > +memory, shmem, tmpfs, etc., whereas pagecache is allocated in an > > > +interleaving fashion over all allowed nodes (hardbindings and > > > +zone_reclaim_mode excluded). > > > + > > > +The assumption is that, when it comes to pagecache, users generally > > > +prefer predictable replacement behavior regardless of NUMA topology > > > +and maximizing the cache's effectiveness in reducing IO over memory > > > +locality. > > > > Isn't page spreading (PF_SPREAD_PAGE) intended to do the same thing > > semantically? The setting is per-cpuset rather than global which makes > > it harder to use but essentially it tries to distribute page cache pages > > across all the nodes. > > > > This is really getting confusing. We have zone_reclaim_mode to keep > > memory local in general, pagecache_mempolicy_mode to keep page cache > > local and PF_SPREAD_PAGE to spread the page cache around nodes. > > zone_reclaim_mode is a global setting to go through great lengths to > stay on local nodes, intended to be used depending on the hardware, > not the workload. > > Mempolicy on the other hand is to optimize placement for maximum > locality depending on access patterns of a workload or even just the > subset of a workload. I'm trying to change whether this applies to > page cache (due to different locality / cache effectiveness tradeoff) > and we want to provide pagecache_mempolicy_mode to revert in the field > in case this is a mistake. > > PF_SPREAD_PAGE becomes implied per default and should eventually be > removed. I guess many loads do not care about page cache locality and the default spreading would be OK for them but what about those that do care? Currently we have a per-process (cpuset in fact) flag but this will change it to all or nothing. Is this really a good step? Btw. I do not mind having PF_SPREAD_PAGE enabled by default. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>