mm, swap: skip swapcache for swapin of synchronous device

With fast swap storage, the platforms want to use swap more aggressively
and swap-in is crucial to application latency.

The rw_page() based synchronous devices like zram, pmem and btt are such
fast storage.  When I profile swapin performance with zram lz4
decompress test, S/W overhead is more than 70%.  Maybe, it would be
bigger in nvdimm.

This patch aims to reduce swap-in latency by skipping swapcache if the
swap device is synchronous device like rw_page based device.  It
enhances 45% my swapin test(5G sequential swapin, no readahead, from
2.41sec to 1.64sec).

Link: http://lkml.kernel.org/r/1505886205-9671-5-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index cb08fa65819f..85aff8a42801 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3455,10 +3455,15 @@ int swapcache_prepare(swp_entry_t entry)
 	return __swap_duplicate(entry, SWAP_HAS_CACHE);
 }
 
+struct swap_info_struct *swp_swap_info(swp_entry_t entry)
+{
+	return swap_info[swp_type(entry)];
+}
+
 struct swap_info_struct *page_swap_info(struct page *page)
 {
-	swp_entry_t swap = { .val = page_private(page) };
-	return swap_info[swp_type(swap)];
+	swp_entry_t entry = { .val = page_private(page) };
+	return swp_swap_info(entry);
 }
 
 /*
@@ -3466,7 +3471,6 @@ struct swap_info_struct *page_swap_info(struct page *page)
  */
 struct address_space *__page_file_mapping(struct page *page)
 {
-	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 	return page_swap_info(page)->swap_file->f_mapping;
 }
 EXPORT_SYMBOL_GPL(__page_file_mapping);
@@ -3474,7 +3478,6 @@ EXPORT_SYMBOL_GPL(__page_file_mapping);
 pgoff_t __page_file_index(struct page *page)
 {
 	swp_entry_t swap = { .val = page_private(page) };
-	VM_BUG_ON_PAGE(!PageSwapCache(page), page);
 	return swp_offset(swap);
 }
 EXPORT_SYMBOL_GPL(__page_file_index);