On Wed, 14 May 2008, Linus Torvalds wrote: > One thing to realize is that most of the time (read: pretty much *always*) > when we have the problem of wanting to sleep inside a spinlock, the > solution is actually to just move the sleeping to outside the lock, and > then have something else that serializes things.
The problem is that the code in rmap.c try_to_umap() and friends loops over reverse maps after taking a spinlock. The mm_struct is only known after the rmap has been acccessed. This means *inside* the spinlock. That is why I tried to convert the locks to scan the revese maps to semaphores. If that is done then one can indeed do the callouts outside of atomic contexts. > Can it be done? I don't know. But I do know that I'm unlikely to accept a > noticeable slowdown in some very core code for a case that affects about > 0.00001% of the population. In other words, I think you *have* to do it. With larger number of processor semaphores make a lot of sense since the holdoff times on spinlocks will increase. If we go to sleep then the processor can do something useful instead of hogging a cacheline. A rw lock there can also increase concurrency during reclaim espcially if the anon_vma chains and the number of address spaces mapping a page is high. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
