Hi, I've spent some time trying to understand why swapoff is such a slow operation.
My experiments show that when there is not much free physical memory, swapoff moves pages out of swap at a rate of approximately 5mb/sec. When there is a lot of free physical memory, it is faster but still a slow CPU-intensive operation, purging swap at about 20mb/sec. I've read into the swap code and I have some understanding that this is an expensive operation (and has to be). This page was very helpful and also agrees: http://kernel.org/doc/gorman/html/understand/understand014.html After reading that, I have an idea for a possible optimization. If we were to create a system call to disable ALL swap partitions (or modify the existing one to accept NULL for that purpose), could this process be signficantly less complex? I'm thinking we could do something like this: 1. Prevent any more pages from being swapped out from this point 2. Iterate through all process page tables, paging all swapped pages back into physical memory and updating PTEs 3. Clear all swap tables and caches Due to only iterating through process page tables once, does this sound like it would increase performance non-trivially? Is it feasible? I'm happy to spend a few more hours looking into implementing this but would greatly appreciate any advice from those in-the-know on if my ideas are broken to start with... Thanks! -- Daniel Drake Brontes Technologies, A 3M Company http://www.brontes3d.com/opensource - 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/
