Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1231189
| From | Greg Thelen <gthelen@google.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] memcg: make mem_cgroup_read_stat() unsigned |
| Date | 2015-09-23 09:30 +0200 |
| Message-ID | <qbMF3-5Lu-7@gated-at.bofh.it> (permalink) |
| References | <qbJxw-1eN-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Andrew Morton wrote: > On Tue, 22 Sep 2015 17:42:13 -0700 Greg Thelen <gthelen@google.com> wrote: > >> Andrew Morton wrote: >> >> > On Tue, 22 Sep 2015 15:16:32 -0700 Greg Thelen <gthelen@google.com> wrote: >> > >> >> mem_cgroup_read_stat() returns a page count by summing per cpu page >> >> counters. The summing is racy wrt. updates, so a transient negative sum >> >> is possible. Callers don't want negative values: >> >> - mem_cgroup_wb_stats() doesn't want negative nr_dirty or nr_writeback. >> >> - oom reports and memory.stat shouldn't show confusing negative usage. >> >> - tree_usage() already avoids negatives. >> >> >> >> Avoid returning negative page counts from mem_cgroup_read_stat() and >> >> convert it to unsigned. >> > >> > Someone please remind me why this code doesn't use the existing >> > percpu_counter library which solved this problem years ago. >> > >> >> for_each_possible_cpu(cpu) >> > >> > and which doesn't iterate across offlined CPUs. >> >> I found [1] and [2] discussing memory layout differences between: >> a) existing memcg hand rolled per cpu arrays of counters >> vs >> b) array of generic percpu_counter >> The current approach was claimed to have lower memory overhead and >> better cache behavior. >> >> I assume it's pretty straightforward to create generic >> percpu_counter_array routines which memcg could use. Possibly something >> like this could be made general enough could be created to satisfy >> vmstat, but less clear. >> >> [1] http://www.spinics.net/lists/cgroups/msg06216.html >> [2] https://lkml.org/lkml/2014/9/11/1057 > > That all sounds rather bogus to me. __percpu_counter_add() doesn't > modify struct percpu_counter at all except for when the cpu-local > counter overflows the configured batch size. And for the memcg > application I suspect we can set the batch size to INT_MAX... Nod. The memory usage will be a bit larger, but the code reuse is attractive. I dusted off Vladimir's https://lkml.org/lkml/2014/9/11/710. Next step is to benchmark it before posting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Re: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Greg Thelen <gthelen@google.com> - 2015-09-23 02:50 +0200
Re: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Andrew Morton <akpm@linux-foundation.org> - 2015-09-23 06:10 +0200
Re: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Greg Thelen <gthelen@google.com> - 2015-09-23 09:30 +0200
Re: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Michal Hocko <mhocko@kernel.org> - 2015-09-25 17:30 +0200
csiph-web