From 796d5116c407690b14fd5bda136aa67a39e7061a Mon Sep 17 00:00:00 2001 From: Jeff Moyer Date: Thu, 2 Jun 2011 21:19:05 +0200 Subject: iosched: prevent aliased requests from starving other I/O Hi, Jens, If you recall, I posted an RFC patch for this back in July of last year: http://lkml.org/lkml/2010/7/13/279 The basic problem is that a process can issue a never-ending stream of async direct I/Os to the same sector on a device, thus starving out other I/O in the system (due to the way the alias handling works in both cfq and deadline). The solution I proposed back then was to start dispatching from the fifo after a certain number of aliases had been dispatched. Vivek asked why we had to treat aliases differently at all, and I never had a good answer. So, I put together a simple patch which allows aliases to be added to the rb tree (it adds them to the right, though that doesn't matter as the order isn't guaranteed anyway). I think this is the preferred solution, as it doesn't break up time slices in CFQ or batches in deadline. I've tested it, and it does solve the starvation issue. Let me know what you think. Cheers, Jeff Signed-off-by: Jeff Moyer Signed-off-by: Jens Axboe --- include/linux/elevator.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/elevator.h b/include/linux/elevator.h index 21a8ebf2dc3..d800d514218 100644 --- a/include/linux/elevator.h +++ b/include/linux/elevator.h @@ -146,7 +146,7 @@ extern struct request *elv_rb_latter_request(struct request_queue *, struct requ /* * rb support functions. */ -extern struct request *elv_rb_add(struct rb_root *, struct request *); +extern void elv_rb_add(struct rb_root *, struct request *); extern void elv_rb_del(struct rb_root *, struct request *); extern struct request *elv_rb_find(struct rb_root *, sector_t); -- cgit v1.2.3