On Sun, 18 Mar 2007 11:35:36 +0000 (GMT) Mel Gorman <[EMAIL PROTECTED]> wrote:
> > But let me leap ahead of myself. > > > >> CONFIG_PAGE_GROUP_BY_MOBILITY > > > > Why does this config item exist? It's not good to have some mysterious > > knob which affects mm behaviour at compile time. We need to make up our > > minds and stick with it. > > > > The configuration item exists because there were concerns over the memory > footprint and cache line footprint. It was introduced to address that > concern and also so that it would be possible to compare the performance > behavior of anti-fragmentation. Your comment rang a bell though so I > searched the archives to see this comment from Andi Kleen; > > === > If anything this should be a boot time option or perhaps sysctl, not a > config. In general CONFIGs that change runtime behaviour are evil - just > makes changing the option more painful, causes problems for distribution > users, doesn't make much sense, etc.etc. > > Also #ifdef as a documentation device is a really really scary concept. > Yuck. > === > > A sysctl would avoid any cache line footprint but not the memory overhead > because the freelists in struct zone as those freelists would still exist. > I could make the option depend on CONFIG_EMBEDDED for the zone overhead. > Would that make sense or would it be preferable to ditch the option > altogether? > > I'll start looking at doing a sysctl so it can be disabled at runtime if > necessary. I strongly suspect that it cannot be enabled again once > disabled but I don't see that as a problem as such. How much additional memory consumption are we expecting here? Whether it's runtime or compile-time, the optionality is not good. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
