en, yes, kmalloc first is better way. since this register_snapshot is not called frequently(only in ctr), the extra overhead brought by always doing kmalloc is minor. but down_write while possible sleep is bad for the do_origin() since it is called by origina_map(). ming On Fri, 2004-11-19 at 15:16, Kevin Corry wrote: > On Friday 19 November 2004 12:36 pm, Ming Zhang wrote: > > yes, i know. semaphore can sleep. but why not release lock, kmalloc, and > > regain lock? i think any code should reduce the chance that make others > > wait for it. especially it hold a write lock, not a read lock. > > Releasing the lock and regaining it means having to search the hash table > all over again to make sure another process hasn't added a new entry for > the same origin. Very wasteful. If we're simply concerned about the amount > of time that we're holding that semaphore, the following patch would do it.
