Messages in this thread | | | Date | Fri, 1 May 2009 16:25:06 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] vmscan: evict use-once pages first (v3) |
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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.
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