swapin_readahead: move and rearrange args

swapin_readahead has never sat well in mm/memory.c: move it to mm/swap_state.c
beside its kindred read_swap_cache_async.  Why were its args in a different
order?  rearrange them.  And since it was always followed by a
read_swap_cache_async of the target page, fold that in and return struct
page*.  Then CONFIG_SWAP=n no longer needs valid_swaphandles and
read_swap_cache_async stubs.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 50 insertions, 48 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 1d803c2d018..ccc9403d535 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1980,48 +1980,6 @@ int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end)
         return 0;
 }
 
-/**
- * swapin_readahead - swap in pages in hope we need them soon
- * @entry: swap entry of this memory
- * @addr: address to start
- * @vma: user vma this addresses belong to
- *
- * Primitive swap readahead code. We simply read an aligned block of
- * (1 << page_cluster) entries in the swap area. This method is chosen
- * because it doesn't cost us any seek time.  We also make sure to queue
- * the 'original' request together with the readahead ones...
- *
- * This has been extended to use the NUMA policies from the mm triggering
- * the readahead.
- *
- * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
- */
-void swapin_readahead(swp_entry_t entry, unsigned long addr,struct vm_area_struct *vma)
-{
-        int nr_pages;
-        struct page *page;
-        unsigned long offset;
-        unsigned long end_offset;
-
-        /*
-         * Get starting offset for readaround, and number of pages to read.
-         * Adjust starting address by readbehind (for NUMA interleave case)?
-         * No, it's very unlikely that swap layout would follow vma layout,
-         * more likely that neighbouring swap pages came from the same node:
-         * so use the same "addr" to choose the same node for each swap read.
-         */
-        nr_pages = valid_swaphandles(entry, &offset);
-        for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
-                /* Ok, do the async read-ahead now */
-                page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
-                                                vma, addr);
-                if (!page)
-                        break;
-                page_cache_release(page);
-        }
-        lru_add_drain();        /* Push any new pages onto the LRU now */
-}
-
 /*
  * We enter with non-exclusive mmap_sem (to exclude vma changes,
  * but allow concurrent faults), and pte mapped but not yet locked.
@@ -2049,8 +2007,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         page = lookup_swap_cache(entry);
         if (!page) {
                 grab_swap_token(); /* Contend for token _before_ read-in */
-                swapin_readahead(entry, address, vma);
-                page = read_swap_cache_async(entry, vma, address);
+                page = swapin_readahead(entry, vma, address);
                 if (!page) {
                         /*
                          * Back out if somebody else faulted in this pte
diff --git a/mm/shmem.c b/mm/shmem.c
index 88c6685f16b..3a22a8f7933 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1036,8 +1036,7 @@ static struct page *shmem_swapin(struct shmem_inode_info *info,
         pvma.vm_pgoff = idx;
         pvma.vm_ops = NULL;
         pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, idx);
-        swapin_readahead(entry, 0, &pvma);
-        page = read_swap_cache_async(entry, &pvma, 0);
+        page = swapin_readahead(entry, &pvma, 0);
         mpol_free(pvma.vm_policy);
         return page;
 }
@@ -1067,8 +1066,7 @@ static inline int shmem_parse_mpol(char *value, int *policy,
 static inline struct page *
 shmem_swapin(struct shmem_inode_info *info,swp_entry_t entry,unsigned long idx)
 {
-        swapin_readahead(entry, 0, NULL);
-        return read_swap_cache_async(entry, NULL, 0);
+        return swapin_readahead(entry, NULL, 0);
 }
 
 static inline struct page *
diff --git a/mm/swap_state.c b/mm/swap_state.c
index b52635601df..668a8042263 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -10,6 +10,7 @@
 #include <linux/mm.h>
 #include <linux/kernel_stat.h>
 #include <linux/swap.h>
+#include <linux/swapops.h>
 #include <linux/init.h>
 #include <linux/pagemap.h>
 #include <linux/buffer_head.h>
@@ -368,3 +369,49 @@ struct page *read_swap_cache_async(swp_entry_t entry,
                 page_cache_release(new_page);
         return found_page;
 }
+
+/**
+ * swapin_readahead - swap in pages in hope we need them soon
+ * @entry: swap entry of this memory
+ * @vma: user vma this address belongs to
+ * @addr: target address for mempolicy
+ *
+ * Returns the struct page for entry and addr, after queueing swapin.
+ *
+ * Primitive swap readahead code. We simply read an aligned block of
+ * (1 << page_cluster) entries in the swap area. This method is chosen
+ * because it doesn't cost us any seek time.  We also make sure to queue
+ * the 'original' request together with the readahead ones...
+ *
+ * This has been extended to use the NUMA policies from the mm triggering
+ * the readahead.
+ *
+ * Caller must hold down_read on the vma->vm_mm if vma is not NULL.
+ */
+struct page *swapin_readahead(swp_entry_t entry,
+                        struct vm_area_struct *vma, unsigned long addr)
+{
+        int nr_pages;
+        struct page *page;
+        unsigned long offset;
+        unsigned long end_offset;
+
+        /*
+         * Get starting offset for readaround, and number of pages to read.
+         * Adjust starting address by readbehind (for NUMA interleave case)?
+         * No, it's very unlikely that swap layout would follow vma layout,
+         * more likely that neighbouring swap pages came from the same node:
+         * so use the same "addr" to choose the same node for each swap read.
+         */
+        nr_pages = valid_swaphandles(entry, &offset);
+        for (end_offset = offset + nr_pages; offset < end_offset; offset++) {
+                /* Ok, do the async read-ahead now */
+                page = read_swap_cache_async(swp_entry(swp_type(entry), offset),
+                                                vma, addr);
+                if (!page)
+                        break;
+                page_cache_release(page);
+        }
+        lru_add_drain();        /* Push any new pages onto the LRU now */
+        return read_swap_cache_async(entry, vma, addr);
+}