On Wed, Jan 18, 2012 at 3:53 PM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Wed, 18 Jan 2012 11:47:03 +0100 > Michal Hocko <mhocko@xxxxxxx> wrote: > >> On Wed 18-01-12 09:12:26, KAMEZAWA Hiroyuki wrote: >> > On Tue, 17 Jan 2012 17:46:05 +0100 >> > Michal Hocko <mhocko@xxxxxxx> wrote: >> > >> > > On Fri 13-01-12 17:40:19, KAMEZAWA Hiroyuki wrote: >> [...] >> > > > This patch removes PCG_MOVE_LOCK and add hashed rwlock array >> > > > instead of it. This works well enough. Even when we need to >> > > > take the lock, >> > > >> > > Hmmm, rwlocks are not popular these days very much. >> > > Anyway, can we rather make it (source) memcg (bit)spinlock instead. We >> > > would reduce false sharing this way and would penalize only pages from >> > > the moving group. >> > > >> > per-memcg spinlock ? >> >> Yes >> >> > The reason I used rwlock() is to avoid disabling IRQ. This routine >> > will be called by IRQ context (for dirty ratio support). So, IRQ >> > disable will be required if we use spinlock. >> >> OK, I have missed the comment about disabling IRQs. It's true that we do >> not have to be afraid about deadlocks if the lock is held only for >> reading from the irq context but does the spinlock makes a performance >> bottleneck? We are talking about the slowpath. >> I could see the reason for the read lock when doing hashed locks because >> they are global but if we make the lock per memcg then we shouldn't >> interfere with other updates which are not blocked by the move. >> > > Hm, ok. In the next version, I'll use per-memcg spinlock (with hash if necessary) Just want to make sure I understand it, even we make the lock per-memcg, there is still a false sharing of pc within one memcg. Do we need to demonstrate the effect ? Also, I don't get the point of why spinlock instead of rwlock in this case? --Ying > > Thanks, > -Kame > > -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
