On Wed, Jun 22, 2011 at 06:46:39PM +0800, Cong Wang wrote: > ??? 2011???06???22??? 17:16, Mel Gorman ??????: > > > >What I meant was that there is a rational reason why 512M is the > >default for enabling THP by default. Tuning it lower than that by any > >means makes very little sense. Tuning it higher might make some sense > >but it is more likely that THP would simply be disabled via sysctl. I > >see very little advantage to introducing this Kconfig option other > >than as a source of confusion when running make oldconfig. > > > > The tunable range is (512, 8192), so 512M is the minimum. > > Sure, I knew it can be disabled via /sys, actually we can do even > more in user-space, that is totally move the 512M check out of kernel, > why we didn't? > Because the reason why 512M is the default is not obvious and there was no guarantee all distros would chose a reasonable default for an init script (or know that an init script was even necessary). This is one of the few cases where there is a sensible default that is the least surprising. > In short, I think we should either remove the 512M from kernel, or > make 512M to be tunable. > That just hands them a different sort of rope to hang themselves with where THP gets enabled on small machines or botting with mem=128M and getting surprised later by the high min_free_kbytes. At this point, I don't really care if the Kconfig entry exists or not. I think it gains nothing but additional confusion for people who write .config files but it's not a topic I want to discuss for days either. -- Mel Gorman 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>