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authorDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>2009-09-21 17:02:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-22 07:17:35 -0700
commit2ca4532a49be92d7b2766c3244b30fa8bfb0114d (patch)
tree1dc838cebacb10317dff78ceccd50b97e24c4f7f /mm/swap_state.c
parent31a5639623a487d6db996c8138c9e53fef2e2d91 (diff)
downloadvexpress-lsk-2ca4532a49be92d7b2766c3244b30fa8bfb0114d.tar.gz
mm: add_to_swap_cache() does not return -EEXIST
After commit 355cfa73 ("mm: modify swap_map and add SWAP_HAS_CACHE flag"), only the context which have set SWAP_HAS_CACHE flag by swapcache_prepare() or get_swap_page() would call add_to_swap_cache(). So add_to_swap_cache() doesn't return -EEXIST any more. Even though it doesn't return -EEXIST, it's not good behavior conceptually to call swapcache_prepare() in the -EEXIST case, because it means clearing SWAP_HAS_CACHE flag while the entry is on swap cache. This patch removes redundant codes and comments from callers of it, and adds VM_BUG_ON() in error path of add_to_swap_cache() and some comments. Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap_state.c')
-rw-r--r--mm/swap_state.c73
1 files changed, 36 insertions, 37 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c
index b076a1a5a0a..6d1daeb1cb4 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -92,6 +92,12 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry)
spin_unlock_irq(&swapper_space.tree_lock);
if (unlikely(error)) {
+ /*
+ * Only the context which have set SWAP_HAS_CACHE flag
+ * would call add_to_swap_cache().
+ * So add_to_swap_cache() doesn't returns -EEXIST.
+ */
+ VM_BUG_ON(error == -EEXIST);
set_page_private(page, 0UL);
ClearPageSwapCache(page);
page_cache_release(page);
@@ -146,38 +152,34 @@ int add_to_swap(struct page *page)
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(!PageUptodate(page));
- for (;;) {
- entry = get_swap_page();
- if (!entry.val)
- return 0;
+ entry = get_swap_page();
+ if (!entry.val)
+ return 0;
+ /*
+ * Radix-tree node allocations from PF_MEMALLOC contexts could
+ * completely exhaust the page allocator. __GFP_NOMEMALLOC
+ * stops emergency reserves from being allocated.
+ *
+ * TODO: this could cause a theoretical memory reclaim
+ * deadlock in the swap out path.
+ */
+ /*
+ * Add it to the swap cache and mark it dirty
+ */
+ err = add_to_swap_cache(page, entry,
+ __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
+
+ if (!err) { /* Success */
+ SetPageDirty(page);
+ return 1;
+ } else { /* -ENOMEM radix-tree allocation failure */
/*
- * Radix-tree node allocations from PF_MEMALLOC contexts could
- * completely exhaust the page allocator. __GFP_NOMEMALLOC
- * stops emergency reserves from being allocated.
- *
- * TODO: this could cause a theoretical memory reclaim
- * deadlock in the swap out path.
- */
- /*
- * Add it to the swap cache and mark it dirty
+ * add_to_swap_cache() doesn't return -EEXIST, so we can safely
+ * clear SWAP_HAS_CACHE flag.
*/
- err = add_to_swap_cache(page, entry,
- __GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);
-
- switch (err) {
- case 0: /* Success */
- SetPageDirty(page);
- return 1;
- case -EEXIST:
- /* Raced with "speculative" read_swap_cache_async */
- swapcache_free(entry, NULL);
- continue;
- default:
- /* -ENOMEM radix-tree allocation failure */
- swapcache_free(entry, NULL);
- return 0;
- }
+ swapcache_free(entry, NULL);
+ return 0;
}
}
@@ -318,14 +320,7 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
break;
}
- /*
- * Associate the page with swap entry in the swap cache.
- * May fail (-EEXIST) if there is already a page associated
- * with this entry in the swap cache: added by a racing
- * read_swap_cache_async, or add_to_swap or shmem_writepage
- * re-using the just freed swap entry for an existing page.
- * May fail (-ENOMEM) if radix-tree node allocation failed.
- */
+ /* 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);
@@ -341,6 +336,10 @@ struct page *read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
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, NULL);
} while (err != -ENOMEM);