On Wed 22-11-23 14:57:24, Huang, Ying wrote: > 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 */ Checking along with folio_test_swapbacked would do the trick, right? -- Michal Hocko SUSE Labs
