Rik van Riel writes: > Rik van Riel wrote: > > Nikita Danilov wrote: > > > >> Probably I am missing something, but I don't see how that can help. For > >> example, suppose (for simplicity) that we have swappiness of 100%, and > >> that fraction of referenced anon pages gets slightly less than of file > >> pages. get_scan_ratio() increases anon_percent, and shrink_zone() starts > >> scanning anon queue more aggressively. As a result, pages spend less > >> time there, and have less chance of ever being accessed, reducing > >> fraction of referenced anon pages further, and triggering further > >> increase in the amount of scanning, etc. Doesn't this introduce positive > >> feed-back loop? > > > > It's a possibility, but I don't think it will be much of an > > issue in practice. > > > > If it is, we can always use refaults as a correcting > > mechanism - which would have the added benefit of being > > able to do streaming IO without putting any pressure on > > the active list, essentially clock-pro replacement with > > just some tweaks to shrink_list()... > > As an aside, due to the use-once algorithm file pages are at a > natural disadvantage already. I believe it would be really > hard to construct a workload where anon pages suffer the positive > feedback loop you describe...
That scenario works for file queues too. Of course, all this is but a theoretical speculation at this point, but I am concerned that - that loop would tend to happen under various border conditions, making it hard to isolate, diagnose, and debug, and - long before it becomes explicitly visible (say, as an excessive cpu consumption by scanner), it would ruin global lru ordering, degrading overall performance. Generally speaking, multi-queue replacement mechanisms were tried in the past, and they all suffer from the common drawback: once scanning rate is different for different queues, so is the notion of "hotness", measured by scanner. As a result multi-queue scanner fails to capture working set properly. Nikita. > > -- > Politics is the struggle between those who want to make their country > the best in the world, and those who believe it already is. Each group > calls the other unpatriotic. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
