Hi Vinayak, On Wed, Sep 11, 2019 at 03:37:23PM +0530, Vinayak Menon wrote: < snip > > >> Can swapcache check be done like below, before taking the SWP_SYNCHRONOUS_IO path, as an alternative ? > > With your approach, what prevent below scenario? > > > > A B > > > > do_swap_page > > SWP_SYNCHRONOUS_IO && __swap_count == 1 > > > As shrink_page_list is picking the page from LRU and B is trying to read from swap simultaneously, I assume someone had read > > the page from swap prior to B, when its swap_count was say 2 (for it to be reclaimed by shrink_page_list now) It could happen after B saw __swap_count == 1. Think about forking new process. In that case, swap_count is 2 and the forked process will access the page(it ends up freeing zram slot but the page would be swap cache. However, B process doesn't know it).
