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.hir...@jp.fujitsu.com> wrote:
> > On Fri, 19 Mar 2010 08:10:39 +0530
> > Balbir Singh <bal...@linux.vnet.ibm.com> wrote:
> >
> >> * KAMEZAWA Hiroyuki <kamezawa.hir...@jp.fujitsu.com> [2010-03-19 10:23:32]:
> >>
> >> > On Thu, 18 Mar 2010 21:58:55 +0530
> >> > Balbir Singh <bal...@linux.vnet.ibm.com> wrote:
> >> >
> >> > > * KAMEZAWA Hiroyuki <kamezawa.hir...@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()?
> if (! trylock_page_cgroup(pc))
> return;
> } else
> lock_page_cgroup(pc);
>
> __mem_cgroup_update_page_stat(pc, idx, charge);
> unlock_page_cgroup(pc);
> }
Vivek
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