> On Fri, 20 Apr 2007 17:52:04 +0200 Peter Zijlstra <[EMAIL PROTECTED]> wrote: > > > Scale writeback cache per backing device, proportional to its writeout > > speed. > > > > By decoupling the BDI dirty thresholds a number of problems we currently > > have > > will go away, namely: > > > > - mutual interference starvation (for any number of BDIs); > > - deadlocks with stacked BDIs (loop, FUSE and local NFS mounts). > > > > It might be that all dirty pages are for a single BDI while other BDIs are > > idling. By giving each BDI a 'fair' share of the dirty limit, each one can > > have > > dirty pages outstanding and make progress. > > > > A global threshold also creates a deadlock for stacked BDIs; when A writes > > to > > B, and A generates enough dirty pages to get throttled, B will never start > > writeback until the dirty pages go away. Again, by giving each BDI its own > > 'independent' dirty limit, this problem is avoided. > > > > So the problem is to determine how to distribute the total dirty limit > > across > > the BDIs fairly and efficiently. A DBI that has a large dirty limit but does > > not have any dirty pages outstanding is a waste. > > > > What is done is to keep a floating proportion between the DBIs based on > > writeback completions. This way faster/more active devices get a larger > > share > > than slower/idle devices. > > This is a pretty major improvement to various nasty corner-cases, if it > works. > > Does it work? Please describe the testing you did, and the results. > > Has this been confirmed to fix Miklos's FUSE and loopback problems?
I haven't yet tested it (will do), but I'm sure it does solve the deadlock in balance_dirty_pages(), if for no other reason, that when the queue is idle (no dirty or writeback pages), then it allowes the caller to dirty some more pages. The other deadlock, in throttle_vm_writeout() is still to be solved. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/