The patch titled vmscan: prevent background aging of anon page in no swap system has been added to the -mm tree. Its filename is vmscan-prevent-background-aging-of-anon-page-in-no-swap-system.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find out what to do about this The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: vmscan: prevent background aging of anon page in no swap system From: Minchan Kim <minchan.kim@xxxxxxxxx> 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-swapon and non-configured swap system. Of course, 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). I used total_swap_pages because we want to age anon pages even though swap full happens. Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Reported-by: Ying Han <yinghan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN mm/vmscan.c~vmscan-prevent-background-aging-of-anon-page-in-no-swap-system mm/vmscan.c --- a/mm/vmscan.c~vmscan-prevent-background-aging-of-anon-page-in-no-swap-system +++ a/mm/vmscan.c @@ -2137,7 +2137,7 @@ loop_again: * Do some background aging of the anon list, to give * pages a chance to be referenced before reclaiming. */ - if (inactive_anon_is_low(zone, &sc)) + if (total_swap_pages > 0 && inactive_anon_is_low(zone, &sc)) shrink_active_list(SWAP_CLUSTER_MAX, zone, &sc, priority, 0); _ Patches currently in -mm which might be from minchan.kim@xxxxxxxxx are vmscan-prevent-background-aging-of-anon-page-in-no-swap-system.patch mm-vmap-area-cache.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html