Messages in this thread | | | From | Nick Piggin <> | Subject | Re: [patch 02/20] make the inode i_mmap_lock a reader/writer lock | Date | Wed, 19 Dec 2007 11:48:06 +1100 |
| |
On Wednesday 19 December 2007 08:15, Rik van Riel wrote: > I have seen soft cpu lockups in page_referenced_file() due to > contention on i_mmap_lock() for different pages. Making the > i_mmap_lock a reader/writer lock should increase parallelism > in vmscan for file back pages mapped into many address spaces. > > Read lock the i_mmap_lock for all usage except: > > 1) mmap/munmap: linking vma into i_mmap prio_tree or removing > 2) unmap_mapping_range: protecting vm_truncate_count > > rmap: try_to_unmap_file() required new cond_resched_rwlock(). > To reduce code duplication, I recast cond_resched_lock() as a > [static inline] wrapper around reworked cond_sched_lock() => > __cond_resched_lock(void *lock, int type). > New cond_resched_rwlock() implemented as another wrapper.
Reader/writer locks really suck in terms of fairness and starvation, especially when the read-side is common and frequent. (also, single threaded performance of the read-side is worse).
I know Lee saw some big latencies on the anon_vma list lock when running (IIRC) a large benchmark... but are there more realistic situations where this is a problem?
| |