On Tue, Jul 05, 2016 at 02:01:29PM -0700, David Rientjes wrote: > On Thu, 30 Jun 2016, Vlastimil Babka wrote: > > > > Note: I really dislike the low watermark check in split_free_page() and > > > consider it poor software engineering. The function should split a free > > > page, nothing more. Terminating memory compaction because of a low > > > watermark check when we're simply trying to migrate memory seems like an > > > arbitrary heuristic. There was an objection to removing it in the first > > > proposed patch, but I think we should really consider removing that > > > check so this is simpler. > > > > There's a patch changing it to min watermark (you were CC'd on the series). We > > could argue whether it belongs to split_free_page() or some wrapper of it, but > > I don't think removing it completely should be done. If zone is struggling > > with order-0 pages, a functionality for making higher-order pages shouldn't > > make it even worse. It's also not that arbitrary, even if we succeeded the > > migration and created a high-order page, the higher-order allocation would > > still fail due to watermark checks. Worse, __compact_finished() would keep > > telling the compaction to continue, creating an even longer lag, which is also > > against your recent patches. > > > > I'm suggesting we shouldn't check any zone watermark in split_free_page(): > that function should just split the free page. > > I don't find our current watermark checks to determine if compaction is > worthwhile to be invalid, but I do think that we should avoid checking or > acting on any watermark in isolate_freepages() itself. We could do more > effective checking in __compact_finished() to determine if we should > terminate compaction, but the freeing scanner feels like the wrong place > to do it -- it's also expensive to check while gathering free pages for > memory that we have already successfully isolated as part of the > iteration. > > Do you have any objection to this fix for 4.7? > > Joonson and/or Minchan, does this address the issue that you reported? Unfortunately, I have no test case to trigger it. But, I think that this patch will address it. Anyway, I commented one problem on this patch in other e-mail so please fix it. Thanks. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html