From 8079b1c859c44f27d63da4951f5038a16589a563 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Wed, 3 Aug 2011 16:21:28 -0700 Subject: mm: clarify the radix_tree exceptional cases Make the radix_tree exceptional cases, mostly in filemap.c, clearer. It's hard to devise a suitable snappy name that illuminates the use by shmem/tmpfs for swap, while keeping filemap/pagecache/radix_tree generality. And akpm points out that /* radix_tree_deref_retry(page) */ comments look like calls that have been commented out for unknown reason. Skirt the naming difficulty by rearranging these blocks to handle the transient radix_tree_deref_retry(page) case first; then just explain the remaining shmem/tmpfs swap case in a comment. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 66 ++++++++++++++++++++++++++++++++++++++++-------------------- 1 file changed, 44 insertions(+), 22 deletions(-) (limited to 'mm/filemap.c') diff --git a/mm/filemap.c b/mm/filemap.c index 96778fa..645a080 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -700,10 +700,14 @@ repeat: if (unlikely(!page)) goto out; if (radix_tree_exception(page)) { - if (radix_tree_exceptional_entry(page)) - goto out; - /* radix_tree_deref_retry(page) */ - goto repeat; + if (radix_tree_deref_retry(page)) + goto repeat; + /* + * Otherwise, shmem/tmpfs must be storing a swap entry + * here as an exceptional entry: so return it without + * attempting to raise page count. + */ + goto out; } if (!page_cache_get_speculative(page)) goto repeat; @@ -838,15 +842,21 @@ repeat: continue; if (radix_tree_exception(page)) { - if (radix_tree_exceptional_entry(page)) - continue; + if (radix_tree_deref_retry(page)) { + /* + * Transient condition which can only trigger + * when entry at index 0 moves out of or back + * to root: none yet gotten, safe to restart. + */ + WARN_ON(start | i); + goto restart; + } /* - * radix_tree_deref_retry(page): - * can only trigger when entry at index 0 moves out of - * or back to root: none yet gotten, safe to restart. + * Otherwise, shmem/tmpfs must be storing a swap entry + * here as an exceptional entry: so skip over it - + * we only reach this from invalidate_mapping_pages(). */ - WARN_ON(start | i); - goto restart; + continue; } if (!page_cache_get_speculative(page)) @@ -904,14 +914,20 @@ repeat: continue; if (radix_tree_exception(page)) { - if (radix_tree_exceptional_entry(page)) - break; + if (radix_tree_deref_retry(page)) { + /* + * Transient condition which can only trigger + * when entry at index 0 moves out of or back + * to root: none yet gotten, safe to restart. + */ + goto restart; + } /* - * radix_tree_deref_retry(page): - * can only trigger when entry at index 0 moves out of - * or back to root: none yet gotten, safe to restart. + * Otherwise, shmem/tmpfs must be storing a swap entry + * here as an exceptional entry: so stop looking for + * contiguous pages. */ - goto restart; + break; } if (!page_cache_get_speculative(page)) @@ -973,13 +989,19 @@ repeat: continue; if (radix_tree_exception(page)) { - BUG_ON(radix_tree_exceptional_entry(page)); + if (radix_tree_deref_retry(page)) { + /* + * Transient condition which can only trigger + * when entry at index 0 moves out of or back + * to root: none yet gotten, safe to restart. + */ + goto restart; + } /* - * radix_tree_deref_retry(page): - * can only trigger when entry at index 0 moves out of - * or back to root: none yet gotten, safe to restart. + * This function is never used on a shmem/tmpfs + * mapping, so a swap entry won't be found here. */ - goto restart; + BUG(); } if (!page_cache_get_speculative(page)) -- cgit v1.1