On 01.06.22 04:11, Miaohe Lin wrote: > On 2022/5/31 20:58, David Hildenbrand wrote: >> On 31.05.22 04:55, Miaohe Lin wrote: >>> On 2022/5/31 7:04, Andrew Morton wrote: >>>> On Fri, 27 May 2022 17:26:25 +0800 Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote: >>>> >>>>> At swapoff time, we're going to swap in the pages continuously. So calling >>>>> lookup_swap_cache would confuse statistics. We should use find_get_page >>>>> directly here. >>>> >>>> Why is the existing behaviour wrong? swapoff() has to swap stuff in to >>>> be able to release the swap device. Why do you believe that this >>>> swapin activity should not be accounted? >>> >>> IMHO, statistics, e.g. swap_cache_info.find_success, are used to show the effectiveness >>> of the swap cache activity. So they should only reflect the memory accessing activity >>> of the user. I think swapoff can't reflect the effectiveness of the swap cache activity >>> because it just swaps in pages one by one. Or statistics should reflect all the activity >>> of the user including swapoff? >> >> I'm wondering who cares and why? > > I thought it's used to show the effectiveness of the swapcache readahead algorithm. If nobody > ever cares about it now, I'm fine to drop this patch. And could these statistics be removed > since nobody cares about it? IIUC, they are printed (via show_swap_cache_info()), which is called via show_free_areas() -- primarily used via show_mem(). show_mem() is primarily used when OOM, when allocation fails and we warn, from the OOM killer, on panic(). I am not sure how useful for (OOM ?) debugging the find_success vs. find_total stats are at all. They are from ancient times. In bb63be0a091c ("tmpfs: move swap_state stats update") we removed other statistics that are "are relics of my 2.4.11 testing". Maybe find_success and find_total can be similarly removed. data_race() indicates to me that these stats are somewhat best-effort already. -- Thanks, David / dhildenb