Vivek Goyal <vgoyal@xxxxxxxxxx> 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@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()) {
> ^^^^^^^^^
> Or may be in_interrupt()?
Good catch. I will replace irqs_disabled() with in_interrupt().
Thank you.
--
Greg
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