On 06/28/2012 04:43 PM, Kamezawa Hiroyuki wrote: > (2012/06/27 6:37), Andrew Morton wrote: >> https://bugzilla.kernel.org/show_bug.cgi?id=43811 >> >> lru_add_drain_all() uses schedule_on_each_cpu(). But >> schedule_on_each_cpu() hangs if a realtime thread is spinning, pinned >> to a CPU. There's no intention to change the scheduler behaviour, so I >> think we should remove schedule_on_each_cpu() from the kernel. >> >> The biggest user of schedule_on_each_cpu() is lru_add_drain_all(). >> >> Does anyone have any thoughts on how we can do this? The obvious >> approach is to declare these: >> >> static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs); >> static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs); >> static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs); >> >> to be irq-safe and use on_each_cpu(). lru_rotate_pvecs is already >> irq-safe and converting lru_add_pvecs and lru_deactivate_pvecs looks >> pretty simple. >> >> Thoughts? >> > > How about this kind of RCU synchronization ? > == > /* > * Double buffered pagevec for quick drain. > * The usual per-cpu-pvec user need to take rcu_read_lock() before > accessing. > * External drainer of pvecs will relpace pvec vector and call > synchroize_rcu(), > * and drain all pages on unused pvecs in turn. > */ > static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS * 2], lru_pvecs); > > atomic_t pvec_idx; /* must be placed onto some aligned address...*/ > > > struct pagevec *my_pagevec(enum lru) > { > return pvec = &__get_cpu_var(lru_pvecs[lru << atomic_read(pvec_idx)]); > } > > /* > * percpu pagevec access should be surrounded by these calls. > */ > static inline void pagevec_start_access() > { > rcu_read_lock(); > } > > static inline void pagevec_end_access() > { > rcu_read_unlock(); > } > > > /* > * changing pagevec array vec 0 <-> 1 > */ > static void lru_pvec_update() > { > if (atomic_read(&pvec_idx)) > atomic_set(&pvec_idx, 0); > else > atomic_set(&pvec_idx, 1); > } > > /* > * drain all LRUS on per-cpu pagevecs. > */ > DEFINE_MUTEX(lru_add_drain_all_mutex); > static void lru_add_drain_all() > { > mutex_lock(&lru_add_drain_mutex); > lru_pvec_update(); > synchronize_rcu(); /* waits for all accessors to pvec quits. */ I don't know RCU internal but conceptually, I understood synchronize_rcu need context switching of all CPU. If it's partly true, it could be a problem, too. > for_each_cpu(cpu) > drain_pvec_of_the_cpu(cpu); > mutex_unlock(&lru_add_drain_mutex); > } > == > > > > > > > > > > > > > > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>