Message ID | 20090609120213.GA18753@attica.americas.sgi.com (mailing list archive) |
---|---|
State | Not Applicable, archived |
Headers | show |
On Tue, 9 Jun 2009 07:02:14 -0500 Robin Holt <holt@sgi.com> wrote: > On Tue, Jun 09, 2009 at 11:37:55AM +0100, Mel Gorman wrote: > > On Tue, Jun 09, 2009 at 04:55:07AM -0500, Robin Holt wrote: > > > On Mon, Jun 08, 2009 at 12:50:48PM +0100, Mel Gorman wrote: > > > > > > Let me start by saying I agree completely with everything you wrote and > > > still disagree with this patch, but was willing to compromise and work > > > around this for our upcoming x86_64 machine by putting a "value add" > > > into our packaging of adding a sysctl that turns reclaim back on. > > > > > > > To be honest, I'm more leaning towards a NACK than an ACK on this one. I > > don't support enough NUMA machines to feel strongly enough about it but > > unconditionally setting zone_reclaim_mode to 0 on x86-64 just because i7's > > might be there seems ill-advised to me and will have other consequences for > > existing more traditional x86-64 NUMA machines. > > I was sort-of planning on coming up with an x86_64 arch specific function > for setting zone_reclaim_mode, but didn't like the direction things > were going. > > Something to the effect of... > --- 20090609.orig/mm/page_alloc.c 2009-06-09 06:51:34.000000000 -0500 > +++ 20090609/mm/page_alloc.c 2009-06-09 06:55:00.160762069 -0500 > @@ -2326,12 +2326,7 @@ static void build_zonelists(pg_data_t *p > while ((node = find_next_best_node(local_node, &used_mask)) >= 0) { > int distance = node_distance(local_node, node); > > - /* > - * If another node is sufficiently far away then it is better > - * to reclaim pages in a zone before going off node. > - */ > - if (distance > RECLAIM_DISTANCE) > - zone_reclaim_mode = 1; > + zone_reclaim_mode = arch_zone_reclaim_mode(distance); > > /* > * We don't want to pressure a particular node. > > And then letting each arch define an arch_zone_reclaim_mode(). If other > values are needed in the determination, we would add parameters to > reflect this. > > For ia64, add > > static inline ia64_zone_reclaim_mode(int distance) > { > if (distance > 15) > return 1; > } > > #define arch_zone_reclaim_mode(_d) ia64_zone_reclaim_mode(_d) > > > Then, inside x86_64_zone_reclaim_mode(), I could make it something like > if (distance > 40 || is_uv_system()) > return 1; > > In the end, I didn't think this fight was worth fighting given how ugly > this felt. Upon second thought, I am beginning to think it is not that > bad, but I also don't think it is that good either. > We've done worse before now... Is it not possible to work out at runtime whether zone reclaim mode is beneficial? Given that zone_reclaim_mode is settable from initscripts, why all the fuss? Is anyone testing RECLAIM_WRITE and RECLAIM_SWAP, btw? The root cause of this problem: having something called "mode". Any time we put a "mode" in the kernel, we get in a mess trying to work out when to set it and to what. I think I'll drop this patch for now.
--- 20090609.orig/mm/page_alloc.c 2009-06-09 06:51:34.000000000 -0500 +++ 20090609/mm/page_alloc.c 2009-06-09 06:55:00.160762069 -0500 @@ -2326,12 +2326,7 @@ static void build_zonelists(pg_data_t *p while ((node = find_next_best_node(local_node, &used_mask)) >= 0) { int distance = node_distance(local_node, node); - /* - * If another node is sufficiently far away then it is better - * to reclaim pages in a zone before going off node. - */ - if (distance > RECLAIM_DISTANCE) - zone_reclaim_mode = 1; + zone_reclaim_mode = arch_zone_reclaim_mode(distance); /* * We don't want to pressure a particular node.