On Wed, 17 Sep 2014, Peter Zijlstra wrote: > On Tue, Sep 16, 2014 at 10:31:24PM -0500, Christoph Lameter wrote: > > On Tue, 16 Sep 2014, Hugh Dickins wrote: > > > > > On the page migration issue: it's not quite as straightforward as > > > Christoph suggests. He and I agree completely that mlocked pages > > > should be migratable, but some real-time-minded people disagree: > > > so normal compaction is still forbidden to migrate mlocked pages in > > > the vanilla kernel (though we in Google patch that prohibition out). > > > So pinning by refcount is no worse for compaction than mlocking, > > > in the vanilla kernel. > > > > Note though that compaction is not the only mechanism that uses page > > migration. True: offhand, I think memory hotremove, and CMA, and explicit mempolicy changes, are all (for good reason) allowed to migrate mlocked pages; but the case which most interests many is migration for compaction. > > Agreed, and not all migration paths check for mlocked iirc. ISTR it is > very much possible for mlocked pages to get migrated in mainline. I think all the checks are for unevictable; and certainly we permit races whereby an mlocked page may miss the unevictable LRU, until subsequent reclaim corrects the omission. But I think that's the extent to which mlocked pages might be migrated for compaction at present. Hugh -- 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>