Messages in this thread |  | | Subject | Re: [PATCH] shows Active/Inactive on per-node meminfo | From | Matthew Dobson <> | Date | Fri, 20 Aug 2004 16:08:26 -0700 |
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On Fri, 2004-08-20 at 15:25, Andrew Morton wrote: > Jesse Barnes <jbarnes@engr.sgi.com> wrote: > > > > On Friday, August 20, 2004 2:48 pm, Jesse Barnes wrote: > > > On Friday, August 20, 2004 2:02 pm, mita akinobu wrote: > > > > + for (i = 0; i < MAX_NR_ZONES; i++) { > > > > + *active += zones[i].nr_active; > > > > + *inactive += zones[i].nr_inactive; > > > > + *free += zones[i].free_pages; > > > > + } > > > > +} > > > > + > > > > - *free += zone->free_pages; > > > > + for_each_pgdat(pgdat) { > > > > + unsigned long l, m, n; > > > > + __get_zone_counts(&l, &m, &n, pgdat); > > > > + *active += l; > > > > + *inactive += m; > > > > + *free += n; > > > > } > > > > > > Just FYI, loops like this are going to be very slow on a large machine. > > > Iterating over every node in the system involves a TLB miss on every > > > iteration along with an offnode reference and possibly cacheline demotion. > > > > ...but I see that you're just adding the info to the per-node meminfo files, > > so it should be ok as long as people access a node's meminfo file from a > > local cpu. /proc/meminfo will still hurt a lot though. > > > > I bring this up because I ran into it once. I created a file > > called /proc/discontig which printed out detailed per-node memory stats, one > > node per line. On a large system it would literally take several seconds to > > cat the file due to the overhead of looking at all the pages and zone > > structures. > > > > So was that an ack, a nack or a quack? > > I'll queue the patch up so it doesn't get lost - could you please take a > closer look at the performance implications sometime, let me know?
It doesn't look like it will have any real impact. The only function (besides reading /proc/meminfo and /sys/devices/system/node/node%d/meminfo files) that is affect by this is get_zone_counts(). get_zone_counts() is already looping over all zones on all nodes in the system anyway, this new code does exactly that. for_each_zone() loops over all the zones by looping through each pgdat in the system, which is what the new code does, but more explicitly. We might do a little better by inlining __get_zone_counts()?
That said, I haven't run any benchmarks or anything... :)
-Matt
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