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authorHugh Dickins <hughd@google.com>2011-08-03 16:21:19 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-08-03 14:25:22 -1000
commita2c16d6cb0e478812829ca84aeabd02e36af35eb (patch)
tree7803a522da5deee7ce753dc5404dca01f42aa176 /mm/filemap.c
parent6328650bb4d854a7dc1498d1c0048b838b0d340c (diff)
downloadlinaro-lsk-a2c16d6cb0e478812829ca84aeabd02e36af35eb.tar.gz
mm: let swap use exceptional entries
If swap entries are to be stored along with struct page pointers in a radix tree, they need to be distinguished as exceptional entries. Most of the handling of swap entries in radix tree will be contained in shmem.c, but a few functions in filemap.c's common code need to check for their appearance: find_get_page(), find_lock_page(), find_get_pages() and find_get_pages_contig(). So as not to slow their fast paths, tuck those checks inside the existing checks for unlikely radix_tree_deref_slot(); except for find_lock_page(), where it is an added test. And make it a BUG in find_get_pages_tag(), which is not applied to tmpfs files. A part of the reason for eliminating shmem_readpage() earlier, was to minimize the places where common code would need to allow for swap entries. The swp_entry_t known to swapfile.c must be massaged into a slightly different form when stored in the radix tree, just as it gets massaged into a pte_t when stored in page tables. In an i386 kernel this limits its information (type and page offset) to 30 bits: given 32 "types" of swapfile and 4kB pagesize, that's a maximum swapfile size of 128GB. Which is less than the 512GB we previously allowed with X86_PAE (where the swap entry can occupy the entire upper 32 bits of a pte_t), but not a new limitation on 32-bit without PAE; and there's not a new limitation on 64-bit (where swap filesize is already limited to 16TB by a 32-bit page offset). Thirty areas of 128GB is probably still enough swap for a 64GB 32-bit machine. Provide swp_to_radix_entry() and radix_to_swp_entry() conversions, and enforce filesize limit in read_swap_header(), just as for ptes. Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Rik van Riel <riel@redhat.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.c49
1 files changed, 31 insertions, 18 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index b83aebfd0a0..76bfb6460f5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -714,9 +714,12 @@ repeat:
page = radix_tree_deref_slot(pagep);
if (unlikely(!page))
goto out;
- if (radix_tree_deref_retry(page))
+ if (radix_tree_exception(page)) {
+ if (radix_tree_exceptional_entry(page))
+ goto out;
+ /* radix_tree_deref_retry(page) */
goto repeat;
-
+ }
if (!page_cache_get_speculative(page))
goto repeat;
@@ -753,7 +756,7 @@ struct page *find_lock_page(struct address_space *mapping, pgoff_t offset)
repeat:
page = find_get_page(mapping, offset);
- if (page) {
+ if (page && !radix_tree_exception(page)) {
lock_page(page);
/* Has the page been truncated? */
if (unlikely(page->mapping != mapping)) {
@@ -849,11 +852,14 @@ repeat:
if (unlikely(!page))
continue;
- /*
- * This can only trigger when the entry at index 0 moves out
- * of or back to the root: none yet gotten, safe to restart.
- */
- if (radix_tree_deref_retry(page)) {
+ if (radix_tree_exception(page)) {
+ if (radix_tree_exceptional_entry(page))
+ continue;
+ /*
+ * 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.
+ */
WARN_ON(start | i);
goto restart;
}
@@ -912,12 +918,16 @@ repeat:
if (unlikely(!page))
continue;
- /*
- * This can only trigger when the entry at index 0 moves out
- * of or back to the root: none yet gotten, safe to restart.
- */
- if (radix_tree_deref_retry(page))
+ if (radix_tree_exception(page)) {
+ if (radix_tree_exceptional_entry(page))
+ break;
+ /*
+ * 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.
+ */
goto restart;
+ }
if (!page_cache_get_speculative(page))
goto repeat;
@@ -977,12 +987,15 @@ repeat:
if (unlikely(!page))
continue;
- /*
- * This can only trigger when the entry at index 0 moves out
- * of or back to the root: none yet gotten, safe to restart.
- */
- if (radix_tree_deref_retry(page))
+ if (radix_tree_exception(page)) {
+ BUG_ON(radix_tree_exceptional_entry(page));
+ /*
+ * 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.
+ */
goto restart;
+ }
if (!page_cache_get_speculative(page))
goto repeat;