lkml.org 
[lkml]   [2007]   [Dec]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch 02/20] make the inode i_mmap_lock a reader/writer lock
Date
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?


\
 
 \ /
  Last update: 2007-12-19 01:51    [from the cache]
©2003-2011 Jasper Spaans