Messages in this thread | | | From | "Huang\, Ying" <> | Subject | Re: [PATCH -mm -v4 08/21] mm, THP, swap: Support to read a huge swap cluster for swapin a THP | Date | Mon, 02 Jul 2018 14:02:47 +0800 |
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Matthew Wilcox <willy@infradead.org> writes:
> 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.
Sure.
>> /* >> * 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 + } else /* swp entry is obsolete ?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?
Can we use -ESTALE instead? The "huge swap cluster is split under us" means the swap entry is kind of "staled".
> 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.
OK. I can change the interface to number of swap entries style to make it more flexible.
> 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)
The encoding method looks good. To use it, we need to
- Encode swap entry and size into swap_entry_size - Call function with swap_entry_size - Decode swap_entry_size to swap entry and size
It appears that there is no real benefit?
Best Regards, Huang, Ying
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