On 07/05/2016 11:01 PM, 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? No. Acked-by: Vlastimil Babka <vbabka@xxxxxxx> > Joonson and/or Minchan, does this address the issue that you reported? > -- 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