> Ying Han reported that backing aging of anon pages in no swap system > causes unnecessary TLB flush. > > When I sent a patch(69c8548175), I wanted this patch but Rik pointed out > and allowed aging of anon pages to give a chance to promote from inactive > to active LRU. > > It has a two problem. > > 1) non-swap system > > Never make sense to age anon pages. > > 2) swap configured but still doesn't swapon > > It doesn't make sense to age anon pages until swap-on time. > But it's arguable. If we have aged anon pages by swapon, VM have moved > anon pages from active to inactive. And in the time swapon by admin, > the VM can't reclaim hot pages so we can protect hot pages swapout. > > But let's think about it. When does swap-on happen? It depends on admin. > we can't expect it. Nonetheless, we have done aging of anon pages to > protect hot pages swapout. It means we lost run time overhead when > below high watermark but gain hot page swap-[in/out] overhead when VM > decide swapout. Is it true? Let's think more detail. > We don't promote anon pages in case of non-swap system. So even though > VM does aging of anon pages, the pages would be in inactive LRU for a long > time. It means many of pages in there would mark access bit again. So access > bit hot/code separation would be pointless. > > This patch prevents unnecessary anon pages demotion in not-yet-swapon and > non-configured swap system. Even, in non-configuared swap system > inactive_anon_is_low can be compiled out. > > It could make side effect that hot anon pages could swap out > when admin does swap on. But I think sooner or later it would be > steady state. So it's not a big problem. > > We could lose someting but gain more thing(TLB flush and unnecessary > function call to demote anon pages). > > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Signed-off-by: Ying Han <yinghan@xxxxxxxxxx> > Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>