On Thu, Sep 06, 2012 at 02:31:12PM +0900, Minchan Kim wrote: > Hi Mel, > > On Wed, Sep 05, 2012 at 11:56:11AM +0100, Mel Gorman wrote: > > On Wed, Sep 05, 2012 at 05:11:13PM +0900, Minchan Kim wrote: > > > This patch introudes MIGRATE_DISCARD mode in migration. > > > It drops *clean cache pages* instead of migration so that > > > migration latency could be reduced by avoiding (memcpy + page remapping). > > > It's useful for CMA because latency of migration is very important rather > > > than eviction of background processes's workingset. In addition, it needs > > > less free pages for migration targets so it could avoid memory reclaiming > > > to get free pages, which is another factor increase latency. > > > > > > > Bah, this was released while I was reviewing the older version. I did > > not read this one as closely but I see the enum problems have gone away > > at least. I'd still prefer if CMA had an additional helper to discard > > some pages with shrink_page_list() and migrate the remaining pages with > > migrate_pages(). That would remove the need to add a MIGRATE_DISCARD > > migrate mode at all. > > I am not convinced with your point. What's the benefit on separating > reclaim and migration? For just removing MIGRATE_DISCARD mode? Maintainability. There are reclaim functions and there are migration functions. Your patch takes migrate_pages() and makes it partially a reclaim function mixing up the responsibilities of migrate.c and vmscan.c. > I don't think it's not bad because my implementation is very simple(maybe > it's much simpler than separating reclaim and migration) and > could be used by others like memory-hotplug in future. They could also have used the helper function from CMA that takes a list of pages, reclaims some and migrates other. > If you're not strong against with me, I would like to insist on my implementation. > I'm not very strongly against it but I'm also very unhappy. -- Mel Gorman SUSE Labs -- 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>