On Wed, Apr 14, 2010 at 2:29 AM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Tue, 13 Apr 2010 23:55:12 -0700 > Greg Thelen <gthelen@xxxxxxxxxx> wrote: >> On Thu, Mar 18, 2010 at 8:00 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> > On Fri, 19 Mar 2010 08:10:39 +0530 >> > Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: >> >> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-03-19 10:23:32]: >> >> >> >> > On Thu, 18 Mar 2010 21:58:55 +0530 >> >> > Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote: >> >> > >> >> > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> [2010-03-18 13:35:27]: >> >> > >> >> > > > Then, no probelm. It's ok to add mem_cgroup_udpate_stat() indpendent from >> >> > > > mem_cgroup_update_file_mapped(). The look may be messy but it's not your >> >> > > > fault. But please write "why add new function" to patch description. >> >> > > > >> >> > > > I'm sorry for wasting your time. >> >> > > >> >> > > Do we need to go down this route? We could check the stat and do the >> >> > > correct thing. In case of FILE_MAPPED, always grab page_cgroup_lock >> >> > > and for others potentially look at trylock. It is OK for different >> >> > > stats to be protected via different locks. >> >> > > >> >> > >> >> > I _don't_ want to see a mixture of spinlock and trylock in a function. >> >> > >> >> >> >> A well documented well written function can help. The other thing is to >> >> of-course solve this correctly by introducing different locking around >> >> the statistics. Are you suggesting the later? >> >> >> > >> > No. As I wrote. >> > - don't modify codes around FILE_MAPPED in this series. >> > - add a new functions for new statistics >> > Then, >> > - think about clean up later, after we confirm all things work as expected. >> >> I have ported Andrea Righi's memcg dirty page accounting patches to latest >> mmtom-2010-04-05-16-09. In doing so I have to address this locking issue. Does >> the following look good? I will (of course) submit the entire patch for review, >> but I wanted make sure I was aiming in the right direction. >> >> void mem_cgroup_update_page_stat(struct page *page, >> enum mem_cgroup_write_page_stat_item idx, bool charge) >> { >> static int seq; >> struct page_cgroup *pc; >> >> if (mem_cgroup_disabled()) >> return; >> pc = lookup_page_cgroup(page); >> if (!pc || mem_cgroup_is_root(pc->mem_cgroup)) >> return; >> >> /* >> * This routine does not disable irq when updating stats. So it is >> * possible that a stat update from within interrupt routine, could >> * deadlock. Use trylock_page_cgroup() to avoid such deadlock. This >> * makes the memcg counters fuzzy. More complicated, or lower >> * performing locking solutions avoid this fuzziness, but are not >> * currently needed. >> */ >> if (irqs_disabled()) { >> if (! trylock_page_cgroup(pc)) >> return; >> } else >> lock_page_cgroup(pc); >> > > I prefer trylock_page_cgroup() always. What is your reason for preferring trylock_page_cgroup()? I assume it's for code simplicity, but I wanted to check. I had though about using trylock_page_cgroup() always, but I think that would make file_mapped accounting even more fuzzy that it already it is. I was trying to retain the current accuracy of file_mapped and only make new counters, like writeback/dirty/etc (those obtained in interrupt), fuzzy. > I have another idea fixing this up _later_. (But I want to start from simple one.) > > My rough idea is following. Similar to your idea which you gave me before. Hi Kame-san, I like the general approach. The code I previously gave you appears to work and is faster than non-root memcgs using mmotm due to mostly being lockless. > == > DEFINE_PERCPU(account_move_ongoing); What's the reason for having a per-cpu account_move_ongoing flag? Would a single system-wide global be sufficient? I assume the majority of the time this value will not be changing because accounting moves are rare. Perhaps all of the per-cpu variables are packed within a per-cpu cacheline making accessing it more likely to be local, but I'm not sure if this is true. -- Greg -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href