On Wed, Feb 19, 2014 at 04:39:47PM -0500, Rik van Riel wrote: > On 02/19/2014 04:27 PM, Andrew Morton wrote: > > On Tue, 18 Feb 2014 16:35:22 -0800 Kelley Nielsen <kelleynnn@xxxxxxxxx> wrote: > > > >> The function try_to_unuse() is of quadratic complexity, with a lot of > >> wasted effort. It unuses swap entries one by one, potentially iterating > >> over all the page tables for all the processes in the system for each > >> one. > >> > >> This new proposed implementation of try_to_unuse simplifies its > >> complexity to linear. It iterates over the system's mms once, unusing > >> all the affected entries as it walks each set of page tables. It also > >> makes similar changes to shmem_unuse. > >> > >> Improvement > >> > >> swapoff was called on a swap partition containing about 50M of data, > >> and calls to the function unuse_pte_range were counted. > >> > >> Present implementation....about 22.5M calls. > >> Prototype.................about 7.0K calls. > > > > Do you have situations in which swapoff is taking an unacceptable > > amount of time? If so, please update the changelog to provide full > > details on this, with before-and-after timing measurements. > > I have seen plenty of that. With just a few GB in swap space in > use, on a system with 24GB of RAM, and about a dozen GB in use > by various processes, I have seen swapoff take several hours of > CPU time. And it's clear what the lower bound on swapoff should be: current amount of swap in use, divided by maximum disk write speed. We're definitely not to *that* point yet; this ought to get us a lot closer. - Josh Triplett -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>