On Thu, Nov 18, 2010 at 11:49:28AM -0800, Andrew Morton wrote: > On Thu, 18 Nov 2010 09:20:44 +0000 > Mel Gorman <mel@xxxxxxxxx> wrote: > > > > It's because migration depends on MMU. But we should be able to make > > > a NOMMU version of migration that just does page cache, which is all > > > that is reclaimable on NOMMU anyway. > > > > > > > Conceivably, but I see little problem leaving them with lumpy reclaim. > > I see a really big problem: we'll need to maintain lumpy reclaim for > ever! > At least as long as !CONFIG_COMPACTION exists. That will be a while because bear in mind CONFIG_COMPACTION is disabled by default (although I believe some distros are enabling it at least). Maybe we should choose to deprecate it in 2.6.40 and delete it at the infamous time of 2.6.42? That would give ample time to iron out any issues that crop up with reclaim/compaction (what this series has turned into). Bear in mind that lumpy reclaim is heavily isolated these days. The logic is almost entirely contained in isolate_lru_pages() in the block starting with the comment "Attempt to take all pages in the order aligned region surrounding the tag page". As disruptive as lumpy reclaim is, it's basically just a linear scanner at the end of the day and there are a few examples of that in the kernel. If we break it, it'll be obvious. > We keep on piling in more and more stuff, we're getting less sure that > the old stuff is still effective. It's becoming more and more > important to move some of our attention over to simplification, and > to rejustification of earlier decisions. > I'm open to its ultimate deletion but think it's rash to do on day 1 of reclaim/compaction. I do recognise that I might be entirely on my own with this opinion though :) -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>