On Fri, Jun 22, 2018 at 11:51:38AM +0800, Huang, Ying wrote: > +++ b/mm/swap_state.c > @@ -426,33 +447,37 @@ struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask, > /* > * call radix_tree_preload() while we can wait. > */ > - err = radix_tree_maybe_preload(gfp_mask & GFP_KERNEL); > + err = radix_tree_maybe_preload_order(gfp_mask & GFP_KERNEL, > + compound_order(new_page)); > if (err) > break; There's no more preloading in the XArray world, so this can just be dropped. > /* > * Swap entry may have been freed since our caller observed it. > */ > + err = swapcache_prepare(hentry, huge_cluster); > + if (err) { > radix_tree_preload_end(); > - break; > + if (err == -EEXIST) { > + /* > + * We might race against get_swap_page() and > + * stumble across a SWAP_HAS_CACHE swap_map > + * entry whose page has not been brought into > + * the swapcache yet. > + */ > + cond_resched(); > + continue; > + } else if (err == -ENOTDIR) { > + /* huge swap cluster is split under us */ > + continue; > + } else /* swp entry is obsolete ? */ > + break; I'm not entirely happy about -ENOTDIR being overloaded to mean this. Maybe we can return a new enum rather than an errno? Also, I'm not sure that a true/false parameter is the right approach for "is this a huge page". I think we'll have usecases for swap entries which are both larger and smaller than PMD_SIZE. I was hoping to encode the swap entry size into the entry; we only need one extra bit to do that (no matter the size of the entry). I detailed the encoding scheme here: https://plus.google.com/117536210417097546339/posts/hvctn17WUZu (let me know if that doesn't work for you; I'm not very experienced with this G+ thing)