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. -- All rights reversed. -- 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>