On Mon, Oct 10, 2011 at 3:58 PM, Andi Kleen <a...@firstfloor.org> wrote: > On Mon, Oct 10, 2011 at 12:20:53PM +0200, Richard Guenther wrote: >> On Sun, Oct 9, 2011 at 9:55 PM, Andi Kleen <a...@firstfloor.org> wrote: >> > From: Andi Kleen <a...@linux.intel.com> >> > >> > Add a threshold to avoid freeing pages back too early to the OS. >> > This avoid virtual memory map fragmentation. >> > >> > Based on a idea from Honza >> >> Less than 20% looks high. Shouldn't ggc-free-min be enough to >> avoid fragmentation? > > It depends on the working set. If there's more to garbage collect > than max(ggc-free-min, threshold*total) a host without MADV_DONTNEED > will get holes. And ggc-free-min isn't very much on a large > build. > > So it seems safer to me to have a threshold which adjusts for large > working sets. What value do you prefer instead of 20%? (or just 0)
I'm not sure honestly - 10% maybe? I realize it's quite arbitrary ... >> >> This will hide gc bugs with always-collect (ggc-checking), so >> the parameter(s) need to be adjusted for that case to always >> give pages back. The current values should probably be printed >> where the two existing ones are printed as well (with -v). > > Will fix. > -Andi >
