On Tue, 13 Apr 2010 23:55:12 -0700 Greg Thelen <[email protected]> wrote:
> On Thu, Mar 18, 2010 at 8:00 PM, KAMEZAWA Hiroyuki > <[email protected]> wrote: > > On Fri, 19 Mar 2010 08:10:39 +0530 > > Balbir Singh <[email protected]> wrote: > > > >> * KAMEZAWA Hiroyuki <[email protected]> [2010-03-19 10:23:32]: > >> > >> > On Thu, 18 Mar 2010 21:58:55 +0530 > >> > Balbir Singh <[email protected]> wrote: > >> > > >> > > * KAMEZAWA Hiroyuki <[email protected]> [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. 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. == DEFINE_PERCPU(account_move_ongoing); DEFINE_MUTEX(move_account_mutex): void memcg_start_account_move(void) { mutex_lock(&move_account_mutex); for_each_online_cpu(cpu) per_cpu(cpu, account_move_ongoing) += 1; mutex_unlock(&move_account_mutex); /* Wait until there are no lockless update */ synchronize_rcu(); return; } void memcg_end_account_move(void) { mutex_lock(&move_account_mutex); for_each_online_cpu(cpu) per_cpu(cpu, account_move_ongoing) -= 1; mutex_unlock(&move_account_mutex); } /* return 1 when we took lock, return 0 if lockess OPs is guarantedd to be safe */ int memcg_start_filecache_accounting(struct page_cgroup *pc) { rcu_read_lock(); smp_rmb(); if (!this_cpu_read(move_account_ongoing)) return 0; /* no move account is ongoing */ lock_page_cgroup(pc); return 1; } void memcg_end_filecache_accounting(struct page_cgroup *pc, int unlock) { if (unlock) unlock_page_cgroup(pc); rcu_read_unlock(); } and call memcg_start_account_move()/end_account_move() in the start/end of migrainting chunk of pages. Bye. -Kame _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
