From 2ca4532a49be92d7b2766c3244b30fa8bfb0114d Mon Sep 17 00:00:00 2001 From: Daisuke Nishimura Date: Mon, 21 Sep 2009 17:02:52 -0700 Subject: [PATCH] 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 Reviewed-by: KAMEZAWA Hiroyuki Cc: Balbir Singh Cc: Hugh Dickins Cc: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/shmem.c | 4 +++ mm/swap_state.c | 75 ++++++++++++++++++++++++------------------------- 2 files changed, 41 insertions(+), 38 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index bd20f8bb02a..376d8f0a8f6 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1097,6 +1097,10 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) shmem_swp_unmap(entry); unlock: spin_unlock(&info->lock); + /* + * add_to_swap_cache() doesn't return -EEXIST, so we can safely + * clear SWAP_HAS_CACHE flag. + */ swapcache_free(swap, NULL); redirty: set_page_dirty(page); 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); + /* + * 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); - 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; - } + if (!err) { /* Success */ + SetPageDirty(page); + return 1; + } else { /* -ENOMEM radix-tree allocation failure */ + /* + * add_to_swap_cache() doesn't return -EEXIST, so we can safely + * clear SWAP_HAS_CACHE flag. + */ + 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);