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Subject[patch 4/10] decouple swapper_space treatment from other address_spaces


swapper_space is different. Its pages are locked during writeout, it
uses PAGE_SIZE rather than PAGE_CACHE_SIZE. Converting swap to look
more like the other address_spaces is a separate project. This patch
fully restores the old swap behaviour.

- Don't dirty swapcache page buffers in set_page_dirty().

Fixes a problem where __free_pte() runs set_page_dirty() and then
immediately runs ClearPageDirty(). The pages ends up clean, with
dirty buffers, and is unfreeable.

- Hence, don't mark the page clean if its buffers are clean - swap
does not have page/buffers dirty state coherency.


=====================================

--- 2.5.13/mm/page-writeback.c~clean-swap-page Sun May 5 13:32:00 2002
+++ 2.5.13-akpm/mm/page-writeback.c Sun May 5 13:32:36 2002
@@ -454,6 +454,9 @@ EXPORT_SYMBOL(write_one_page);
*
* FIXME: may need to call ->reservepage here as well. That's rather up to the
* address_space though.
+ *
+ * For now, we treat swapper_space specially. It doesn't use the normal
+ * block a_ops.
*/
int __set_page_dirty_buffers(struct page *page)
{
@@ -470,7 +473,7 @@ int __set_page_dirty_buffers(struct page

spin_lock(&inode->i_bufferlist_lock);

- if (page_has_buffers(page)) {
+ if (page_has_buffers(page) && !PageSwapCache(page)) {
struct buffer_head *head = page_buffers(page);
struct buffer_head *bh = head;

--- 2.5.13/fs/buffer.c~clean-swap-page Sun May 5 13:32:00 2002
+++ 2.5.13-akpm/fs/buffer.c Sun May 5 13:32:36 2002
@@ -2159,14 +2159,6 @@ static void check_ttfb_buffer(struct pag
* total exclusion from __set_page_dirty_buffers(). That is obtained with
* i_bufferlist_lock.
*
- * Nobody should be calling try_to_free_buffers against a page which is
- * eligible for set_page_dirty() treatment anyway - the page is clearly
- * not freeable. So we could just test page_count(page) here and complain
- * then scram if it's wrong.
- *
- * If any buffer is not uptodate then the entire page is set not uptodate,
- * as the partial uptodateness information is about to be lost.
- *
* try_to_free_buffers() is non-blocking.
*/
static inline int buffer_busy(struct buffer_head *bh)
@@ -2222,8 +2214,17 @@ int try_to_free_buffers(struct page *pag
inode = page->mapping->host;
spin_lock(&inode->i_bufferlist_lock);
ret = drop_buffers(page);
- if (ret)
+ if (ret && !PageSwapCache(page)) {
+ /*
+ * If the filesystem writes its buffers by hand (eg ext3)
+ * then we can have clean buffers against a dirty page. We
+ * clean the page here; otherwise later reattachment of buffers
+ * could encounter a non-uptodate page, which is unresolvable.
+ * This only applies in the rare case where try_to_free_buffers
+ * succeeds but the page is not freed.
+ */
ClearPageDirty(page);
+ }
spin_unlock(&inode->i_bufferlist_lock);
return ret;
}

-
-
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