On Fri, Mar 17, 2023 at 03:19:09AM -0700, Yosry Ahmed wrote: > > Now, we will not drop the swap cache even if the swap count becomes 0 if > > swap space utility < 50%. Per my understanding, this avoid swap page > > writing for read accesses. So I don't think we can change this directly > > without necessary discussion firstly. > > > Right. I am not sure I understand why we do this today, is it to save > the overhead of allocating a new swap entry if the page is swapped out > again soon? I am not sure I understand this statement "this avoid swap > page > writing for read accesses". When the page is swapped out again soon. If the swap slot has been recycled, then the page need to assign to a new swap slot, most likely different than the previous slot. Then the page write out would need to write that page to the swap device, even though that swap device might already has the same page data in the previous slot. If keeping the previous swap slot cache when swap space utility < 50%, then the swap code can avoid writing out to the same slot with the same data, if the page is not dirty (read only access). The saving is in 1) avoid allocating a new slot. 2) For read access, avoid page io write the same data to the same slot. Chris
