Jan Kara wrote: > > Chris Snook wrote: > > > Al Boldi wrote: > > > > This RFC proposes to introduce a tunable which allows to disable > > > > fsync and changes ordered into writeback writeout on a per-process > > > > basis like this: > > > > > > > > echo 1 > /proc/`pidof process`/softsync > > > > > > This is basically a kernel workaround for stupid app behavior. > > > > Exactly right to some extent, but don't forget the underlying > > data=ordered starvation problem, which looks like a genuinely deep > > problem maybe related to blockIO. > > It is a problem with the way how ext3 does fsync (at least that's what > we ended up with in that konqueror problem)... It has to flush the > current transaction which means that app doing fsync() has to wait till > all dirty data of all files on the filesystem are written (if we are in > ordered mode). And that takes quite some time... There are possibilities > how to avoid that but especially with freshly created files, it's tough > and I don't see a way how to do it without some fundamental changes to > JBD. Ok, but keep in mind that this starvation occurs even in the absence of fsync, as the benchmarks show. And, a quick test of successive 1sec delayed syncs shows no hangs until about 1 minute (~180mb) of db-writeout activity, when the sync abruptly hangs for minutes on end, and io-wait shows almost 100%. Now it turns out that 'echo 3 > /proc/.../drop_caches' has no effect, but doing it a few more times makes the hangs go away for while, only to come back again and again. Thanks! -- Al - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
