On Thu, 2007-04-05 at 15:57 -0700, Andrew Morton wrote: > On Thu, 05 Apr 2007 19:42:19 +0200 > [EMAIL PROTECTED] wrote: > > > Introduce a mechanism to wait on free memory. > > > > Currently congestion_wait() is abused to do this. > > Such a very small explanation for such a terrifying change.
Yes, I suck at writing changelogs, bad me. Normally I would take a day to write them, but I just wanted to get this code out there. Perhaps a bad decision. > > ... > > > > --- linux-2.6-mm.orig/mm/vmscan.c 2007-04-05 16:29:46.000000000 +0200 > > +++ linux-2.6-mm/mm/vmscan.c 2007-04-05 16:29:49.000000000 +0200 > > @@ -1436,6 +1436,7 @@ static int kswapd(void *p) > > finish_wait(&pgdat->kswapd_wait, &wait); > > > > balance_pgdat(pgdat, order); > > + page_alloc_ok(); > > } > > return 0; > > } > > For a start, we don't know that kswapd freed pages which are in a suitable > zone. And we don't know that kswapd freed pages which are in a suitable > cpuset. > > congestion_wait() is similarly ignorant of the suitability of the pages, > but the whole idea behind congestion_wait is that it will throttle page > allocators to some speed which is proportional to the speed at which the IO > systems can retire writes - view it as a variable-speed polling operation, > in which the polling frequency goes up when the IO system gets faster. > This patch changes that philosophy fundamentally. That's worth more than a > 2-line changelog. > > Also, there might be situations in which kswapd gets stuck in some dark > corner. Perhaps the process which is waiting in the page allocator holds > filesystem locks which kswapd is blocked on. Or kswapd might be blocked on > a particular request queue, or a dead NFS server or something. The timeout > will save us, but things will be slow. > > There could be other problems too, dunno - this stuff is tricky. Why are > you changing it, what problems are being solved, etc? Lets start with the why, because of 12/12; I wanted to introduce per BDI congestion feedback, and hence needed a BDI context for congestion_wait(). These specific callers weren't in the context of a BDI but of a more global idea. Perhaps I could call page_alloc_ok() from bdi_congestion_end() irrespective of the actual BDI uncongested? That would more or less give the old semantics. - 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/