On Fri, Mar 20, 2015 at 03:17:03PM -0700, Andrew Morton wrote: > On Fri, 20 Mar 2015 09:49:50 -0400 Eric B Munson <emunson@xxxxxxxxxx> wrote: > > > Currently, pages which are marked as unevictable are protected from > > compaction, but not from other types of migration. The POSIX real time > > extension explicitly states that mlock() will prevent a major page > > fault, but the spirit of this is that mlock() should give a process the > > ability to control sources of latency, including minor page faults. > > However, the mlock manpage only explicitly says that a locked page will > > not be written to swap and this can cause some confusion. The > > compaction code today does not give a developer who wants to avoid swap > > but wants to have large contiguous areas available any method to achieve > > this state. This patch introduces a sysctl for controlling compaction > > behavior with respect to the unevictable lru. Users that demand no page > > faults after a page is present can set compact_unevictable_allowed to 0 > > and users who need the large contiguous areas can enable compaction on > > locked memory by leaving the default value of 1. > > Do we really really really need the /proc knob? We're already > migrating these pages so users of mlock will occasionally see some > latency - how likely is it that this patch will significantly damage > anyone? -rt disables everything that causes those migrations (with exception of sys_migrate_pages). And like I've argued before; mlock() is part of the posix real-time extensions and the real-time people really do not want those migrations. And while the letter of the posix spec allows migrations, the spirit clearly does not. -- 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>