mm: swap: zswap: maybe_preload & refactoring

zswap_get_swap_cache_page and read_swap_cache_async have pretty much the
same code with only significant difference in return value and usage of
swap_readpage.

I a helper __read_swap_cache_async() with the common code.  Behavior
change: now zswap_get_swap_cache_page will use radix_tree_maybe_preload
instead radix_tree_preload.  Looks like, this wasn't changed only by the
reason of code duplication.

Signed-off-by: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@fb.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Seth Jennings <sjennings@variantweb.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 2ce1907..7ba7dcc 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -406,6 +406,9 @@ extern void free_pages_and_swap_cache(struct page **, int);
 extern struct page *lookup_swap_cache(swp_entry_t);
 extern struct page *read_swap_cache_async(swp_entry_t, gfp_t,
                        struct vm_area_struct *vma, unsigned long addr);
+extern struct page *__read_swap_cache_async(swp_entry_t, gfp_t,
+                       struct vm_area_struct *vma, unsigned long addr,
+                       bool *new_page_allocated);
 extern struct page *swapin_readahead(swp_entry_t, gfp_t,
                        struct vm_area_struct *vma, unsigned long addr);
 

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 8bc8e66..d504adb 100644 (file)
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -288,17 +288,14 @@ struct page * lookup_swap_cache(swp_entry_t entry)
        return page;
 }
 
-/* 
- * Locate a page of swap in physical memory, reserving swap cache space
- * and reading the disk if it is not already cached.
- * A failure return means that either the page allocation failed or that
- * the swap entry is no longer in use.
- */
-struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
-                       struct vm_area_struct *vma, unsigned long addr)
+struct page *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
+                       struct vm_area_struct *vma, unsigned long addr,
+                       bool *new_page_allocated)
 {
        struct page *found_page, *new_page = NULL;
+       struct address_space *swapper_space = swap_address_space(entry);
        int err;
+       *new_page_allocated = false;
 
        do {
                /*
@@ -306,8 +303,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                 * called after lookup_swap_cache() failed, re-calling
                 * that would confuse statistics.
                 */
-               found_page = find_get_page(swap_address_space(entry),
-                                       entry.val);
+               found_page = find_get_page(swapper_space, entry.val);
                if (found_page)
                        break;
 
@@ -366,7 +362,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
                         * Initiate read into locked page and return.
                         */
                        lru_cache_add_anon(new_page);
-                       swap_readpage(new_page);
+                       *new_page_allocated = true;
                        return new_page;
                }
                radix_tree_preload_end();
@@ -384,6 +380,25 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
        return found_page;
 }
 
+/*
+ * Locate a page of swap in physical memory, reserving swap cache space
+ * and reading the disk if it is not already cached.
+ * A failure return means that either the page allocation failed or that
+ * the swap entry is no longer in use.
+ */
+struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
+                       struct vm_area_struct *vma, unsigned long addr)
+{
+       bool page_was_allocated;
+       struct page *retpage = __read_swap_cache_async(entry, gfp_mask,
+                       vma, addr, &page_was_allocated);
+
+       if (page_was_allocated)
+               swap_readpage(retpage);
+
+       return retpage;
+}
+
 static unsigned long swapin_nr_pages(unsigned long offset)
 {
        static unsigned long prev_offset;

diff --git a/mm/zswap.c b/mm/zswap.c
index 2d5727b..09208c7 100644 (file)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -446,75 +446,14 @@ enum zswap_get_swap_ret {
 static int zswap_get_swap_cache_page(swp_entry_t entry,
                                struct page **retpage)
 {
-       struct page *found_page, *new_page = NULL;
-       struct address_space *swapper_space = swap_address_space(entry);
-       int err;
+       bool page_was_allocated;
 
-       *retpage = NULL;
-       do {
-               /*
-                * First check the swap cache.  Since this is normally
-                * called after lookup_swap_cache() failed, re-calling
-                * that would confuse statistics.
-                */
-               found_page = find_get_page(swapper_space, entry.val);
-               if (found_page)
-                       break;
-
-               /*
-                * Get a new page to read into from swap.
-                */
-               if (!new_page) {
-                       new_page = alloc_page(GFP_KERNEL);
-                       if (!new_page)
-                               break; /* Out of memory */
-               }
-
-               /*
-                * call radix_tree_preload() while we can wait.
-                */
-               err = radix_tree_preload(GFP_KERNEL);
-               if (err)
-                       break;
-
-               /*
-                * Swap entry may have been freed since our caller observed it.
-                */
-               err = swapcache_prepare(entry);
-               if (err == -EEXIST) { /* seems racy */
-                       radix_tree_preload_end();
-                       continue;
-               }
-               if (err) { /* swp entry is obsolete ? */
-                       radix_tree_preload_end();
-                       break;
-               }
-
-               /* May fail (-ENOMEM) if radix-tree node allocation failed. */
-               __set_page_locked(new_page);
-               SetPageSwapBacked(new_page);
-               err = __add_to_swap_cache(new_page, entry);
-               if (likely(!err)) {
-                       radix_tree_preload_end();
-                       lru_cache_add_anon(new_page);
-                       *retpage = new_page;
-                       return ZSWAP_SWAPCACHE_NEW;
-               }
-               radix_tree_preload_end();
-               ClearPageSwapBacked(new_page);
-               __clear_page_locked(new_page);
-               /*
-                * add_to_swap_cache() doesn't return -EEXIST, so we can safely
-                * clear SWAP_HAS_CACHE flag.
-                */
-               swapcache_free(entry);
-       } while (err != -ENOMEM);
-
-       if (new_page)
-               page_cache_release(new_page);
-       if (!found_page)
+       *retpage = __read_swap_cache_async(entry, GFP_KERNEL,
+                       NULL, 0, &page_was_allocated);
+       if (page_was_allocated)
+               return ZSWAP_SWAPCACHE_NEW;
+       if (!*retpage)
                return ZSWAP_SWAPCACHE_FAIL;
-       *retpage = found_page;
        return ZSWAP_SWAPCACHE_EXIST;
 }