On Fri 05-07-19 20:45:05, Kuo-Hsin Yang wrote: > With 4 processes accessing non-overlapping parts of a large file, 30316 > pages swapped out with this patch, 5152 pages swapped out without this > patch. The swapout number is small comparing to pgpgin.
which is 5 times more swapout. This may be seen to be a lot for workloads that prefer no swapping (e.g. large in memory databases) with an occasional heavy IO (e.g. backup). And I am worried those would regress. I do agree that the current behavior is far from optimal because the trashing is real. I believe that we really need a different approach. Johannes has brought this up few years back (sorry I do not have a link handy) but it was essentially about implementing refault logic to anonymous memory and swap out based on the refault price. If there is effectively no swapin then it simply makes more sense to swap out rather than refault a page cache. That being said, I am not nacking the patch. Let's see whether something regresses as there is a no clear cut for the proper behavior. But I am bringing that up because we really need a better and more robust plan for the future. -- Michal Hocko SUSE Labs