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| author | Hugh Dickins <hughd@google.com> | 2011-08-04 01:21:28 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-08-04 02:25:24 +0200 |
| commit | 8079b1c859c44f27d63da4951f5038a16589a563 (patch) | |
| tree | 677e77a4c9d3b9c33427196cb5f860ebcf530b15 /mm/filemap.c | |
| parent | tmpfs radix_tree: locate_item to speed up swapoff (diff) | |
| download | linux-8079b1c859c44f27d63da4951f5038a16589a563.tar.xz linux-8079b1c859c44f27d63da4951f5038a16589a563.zip | |
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 <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/filemap.c')
| -rw-r--r-- | mm/filemap.c | 66 |
1 files changed, 44 insertions, 22 deletions
diff --git a/mm/filemap.c b/mm/filemap.c index 96778faf82d5..645a080ba4df 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)) |