Yosry Ahmed <yosryahmed@xxxxxxxxxx> writes: > On Tue, Nov 21, 2023 at 10:41 PM Liu Shixin <liushixin2@xxxxxxxxxx> wrote: >> >> >> On 2023/11/21 21:00, Michal Hocko wrote: >> > On Tue 21-11-23 17:06:24, Liu Shixin wrote: >> > >> > However, in swapcache_only mode, the scan count still increased when scan >> > non-swapcache pages because there are large number of non-swapcache pages >> > and rare swapcache pages in swapcache_only mode, and if the non-swapcache >> > is skipped and do not count, the scan of pages in isolate_lru_folios() can >> > eventually lead to hung task, just as Sachin reported [2]. >> > I find this paragraph really confusing! I guess what you meant to say is >> > that a real swapcache_only is problematic because it can end up not >> > making any progress, correct? >> This paragraph is going to explain why checking swapcache_only after scan += nr_pages; >> > >> > AFAIU you have addressed that problem by making swapcache_only anon LRU >> > specific, right? That would be certainly more robust as you can still >> > reclaim from file LRUs. I cannot say I like that because swapcache_only >> > is a bit confusing and I do not think we want to grow more special >> > purpose reclaim types. Would it be possible/reasonable to instead put >> > swapcache pages on the file LRU instead? >> It looks like a good idea, but I'm not sure if it's possible. I can try it, is there anything to >> pay attention to? > > I think this might be more intrusive than we think. Every time a page > is added to or removed from the swap cache, we will need to move it > between LRUs. All pages on the anon LRU will need to go through the > file LRU before being reclaimed. I think this might be too big of a > change to achieve this patch's goal. We need to identify swap cache pages on file LRU firstly. It appears hard from the current definition of page flags. /* Filesystems */ PG_checked = PG_owner_priv_1, /* SwapBacked */ PG_swapcache = PG_owner_priv_1, /* Swap page: swp_entry_t in private */ -- Best Regards, Huang, Ying
