Messages in this thread | | | Date | Sun, 3 May 2009 09:28:06 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH] vmscan: evict use-once pages first (v3) |
| |
On Fri, May 01, 2009 at 04:25:06PM -0700, Andrew Morton wrote: > On Fri, 01 May 2009 19:05:21 -0400 > Rik van Riel <riel@redhat.com> wrote: > > > Andrew Morton wrote: > > > On Wed, 29 Apr 2009 13:14:36 -0400 > > > Rik van Riel <riel@redhat.com> wrote: > > > > > >> When the file LRU lists are dominated by streaming IO pages, > > >> evict those pages first, before considering evicting other > > >> pages. > > >> > > >> This should be safe from deadlocks or performance problems > > >> because only three things can happen to an inactive file page: > > >> 1) referenced twice and promoted to the active list > > >> 2) evicted by the pageout code > > >> 3) under IO, after which it will get evicted or promoted > > >> > > >> The pages freed in this way can either be reused for streaming > > >> IO, or allocated for something else. If the pages are used for > > >> streaming IO, this pageout pattern continues. Otherwise, we will > > >> fall back to the normal pageout pattern. > > >> > > >> .. > > >> > > >> +int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg) > > >> +{ > > >> + unsigned long active; > > >> + unsigned long inactive; > > >> + > > >> + inactive = mem_cgroup_get_local_zonestat(memcg, LRU_INACTIVE_FILE); > > >> + active = mem_cgroup_get_local_zonestat(memcg, LRU_ACTIVE_FILE); > > >> + > > >> + return (active > inactive); > > >> +} > > > > > > This function could trivially be made significantly more efficient by > > > changing it to do a single pass over all the zones of all the nodes, > > > rather than two passes. > > > > How would I do that in a clean way? > > copy-n-paste :( > > static unsigned long foo(struct mem_cgroup *mem, > enum lru_list idx1, enum lru_list idx2) > { > int nid, zid; > struct mem_cgroup_per_zone *mz; > u64 total = 0; > > for_each_online_node(nid) > for (zid = 0; zid < MAX_NR_ZONES; zid++) { > mz = mem_cgroup_zoneinfo(mem, nid, zid); > total += MEM_CGROUP_ZSTAT(mz, idx1); > total += MEM_CGROUP_ZSTAT(mz, idx3); > } > return total; > } > > dunno if that's justifiable. > > > The function mem_cgroup_inactive_anon_is_low and > > the global versions all do the same. It would be > > nice to make all four of them go fast :) > > > > If there is no standardized infrastructure for > > getting multiple statistics yet, I can probably > > whip something up. > > It depends how often it would be called for, I guess. > > One approach would be pass in a variable-length array of `enum > lru_list's, get returned a same-lengthed array of totals. > > Or perhaps all we need to return is the sum of those totals. > > I'd let the memcg guys worry about this if I were you ;) > > > Optimizing them might make sense if it turns out to > > use a significant amount of CPU. > > Yeah. By then it's often too late though. The sort of people for whom > (num_online_nodes*MAX_NR_ZONES) is nuttily large tend not to run > kernel.org kernels.
Good point. We could add a flag that is tested frequently in shrink_list() and updated less frequently in shrink_zone() (or whatever).
| |