Messages in this thread | | | Date | Thu, 15 Apr 2010 11:40:22 +0900 | From | Daisuke Nishimura <> | Subject | Re: [PATCH -mmotm 1/5] memcg: disable irq at page cgroup lock |
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On Wed, 14 Apr 2010 13:14:07 -0700, Greg Thelen <gthelen@google.com> wrote: > Vivek Goyal <vgoyal@redhat.com> writes: > > > On Tue, Apr 13, 2010 at 11:55:12PM -0700, Greg Thelen wrote: > >> On Thu, Mar 18, 2010 at 8:00 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > >> > On Fri, 19 Mar 2010 08:10:39 +0530 > >> > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > >> > > >> >> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [2010-03-19 10:23:32]: > >> >> > >> >> > On Thu, 18 Mar 2010 21:58:55 +0530 > >> >> > Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > >> >> > > >> >> > > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> [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()) { > > ^^^^^^^^^ > > Or may be in_interrupt()? > > Good catch. I will replace irqs_disabled() with in_interrupt(). > I think you should check both. __remove_from_page_cache(), which will update DIRTY, is called with irq disabled(iow, under mapping->tree_lock) but not in interrupt context.
Anyway, I tend to agree with KAMEZAWA-san: use trylock always(except for FILE_MAPPED), or add some new interfaces(e.g. mem_cgroup_update_stat_locked/safe...).
Thanks, Daisuke Nishimura. -- 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/
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