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Commit 2ca4532a authored by Daisuke Nishimura's avatar Daisuke Nishimura Committed by Linus Torvalds
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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: default avatarDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: default avatarKAMEZAWA 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 31a56396

mm/shmem.c

+4 −0
Original line number Diff line number Diff line
@@ -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);

mm/swap_state.c

+36 −37
Original line number Diff line number Diff line
@@ -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);
@@ -146,7 +152,6 @@ 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;
@@ -165,21 +170,18 @@ int add_to_swap(struct page *page) 
	err = add_to_swap_cache(page, entry,

			__GFP_HIGH|__GFP_NOMEMALLOC|__GFP_NOWARN);



		switch (err) {

		case 0:				/* Success */

	if (!err) {	/* 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 */

	} 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;

	}

}

}



/*

 * This must be called only on pages that have
@@ -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);