PATCH: Rewrite of truncate_inode_pages (take 4)

["Juan J. Quintela" <quintela@fi.udc.es>]

>>>>> "juan" == Juan J Quintela <quintela@fi.udc.es> writes:

Hi Linus
   I am resending to you this patch, it works here, and nobody has
   complained about it the previous times that I post it here.
    
Later, Juan.

juan>         I have reworte the function truncate_inode_pages.  The version
juan>         in vanilla pre9-3 does busy waiting in the partial page, with
juan>         this version the locking for the partial page and from the
juan>         rest of the pages is the same.  This make that we have less
juan>         special cases.  For the rest of pages the function works the
juan>         same.  The only difference is that version is cleaner IMHO.
juan>         Or there are some corner case that I have failed to see?

juan>         Comments?

juan>         Later, Juan.

juan>         I have CC: the linux-fsdevel people, they are the users of
juan>         that function, could somebody give me some feedback against
juan>         the change?



diff -urN --exclude-from=/home/lfcia/quintela/work/kernel/exclude work/mm/filemap.c testing/mm/filemap.c
--- work/mm/filemap.c	Fri May 12 23:46:46 2000
+++ testing/mm/filemap.c	Sun May 14 22:08:45 2000
@@ -146,9 +146,39 @@
 	spin_unlock(&pagecache_lock);
 }
 
-/*
+static inline void truncate_partial_page(struct page *page, unsigned partial)
+{
+	memclear_highpage_flush(page, partial, PAGE_CACHE_SIZE-partial);
+				
+	if (page->buffers)
+		block_flushpage(page, partial);
+
+}
+
+static inline void truncate_complete_page(struct page *page)
+{
+	if (!page->buffers || block_flushpage(page, 0))
+		lru_cache_del(page);
+	
+	/*
+	 * We remove the page from the page cache _after_ we have
+	 * destroyed all buffer-cache references to it. Otherwise some
+	 * other process might think this inode page is not in the
+	 * page cache and creates a buffer-cache alias to it causing
+	 * all sorts of fun problems ...  
+	 */
+	remove_inode_page(page);
+	page_cache_release(page);
+}
+
+/**
+ * truncate_inode_pages - truncate *all* the pages from an offset
+ * @mapping: mapping to truncate
+ * @lstart: offset from with to truncate
+ *
  * Truncate the page cache at a set offset, removing the pages
  * that are beyond that offset (and zeroing out partial pages).
+ * If any page is locked we wait for it to become unlocked.
  */
 void truncate_inode_pages(struct address_space * mapping, loff_t lstart)
 {
@@ -168,11 +198,10 @@
 
 		page = list_entry(curr, struct page, list);
 		curr = curr->next;
-
 		offset = page->index;
 
-		/* page wholly truncated - free it */
-		if (offset >= start) {
+		/* Is one of the pages to truncate? */
+		if ((offset >= start) || (partial && (offset + 1) == start)) {
 			if (TryLockPage(page)) {
 				page_cache_get(page);
 				spin_unlock(&pagecache_lock);
@@ -183,22 +212,14 @@
 			page_cache_get(page);
 			spin_unlock(&pagecache_lock);
 
-			if (!page->buffers || block_flushpage(page, 0))
-				lru_cache_del(page);
-
-			/*
-			 * We remove the page from the page cache
-			 * _after_ we have destroyed all buffer-cache
-			 * references to it. Otherwise some other process
-			 * might think this inode page is not in the
-			 * page cache and creates a buffer-cache alias
-			 * to it causing all sorts of fun problems ...
-			 */
-			remove_inode_page(page);
+			if (partial && (offset + 1) == start) {
+				truncate_partial_page(page, partial);
+				partial = 0;
+			} else 
+				truncate_complete_page(page);
 
 			UnlockPage(page);
 			page_cache_release(page);
-			page_cache_release(page);
 
 			/*
 			 * We have done things without the pagecache lock,
@@ -209,37 +230,6 @@
 			 */
 			goto repeat;
 		}
-		/*
-		 * there is only one partial page possible.
-		 */
-		if (!partial)
-			continue;
-
-		/* and it's the one preceeding the first wholly truncated page */
-		if ((offset + 1) != start)
-			continue;
-
-		/* partial truncate, clear end of page */
-		if (TryLockPage(page)) {
-			spin_unlock(&pagecache_lock);
-			goto repeat;
-		}
-		page_cache_get(page);
-		spin_unlock(&pagecache_lock);
-
-		memclear_highpage_flush(page, partial, PAGE_CACHE_SIZE-partial);
-		if (page->buffers)
-			block_flushpage(page, partial);
-
-		partial = 0;
-
-		/*
-		 * we have dropped the spinlock so we have to
-		 * restart.
-		 */
-		UnlockPage(page);
-		page_cache_release(page);
-		goto repeat;
 	}
 	spin_unlock(&pagecache_lock);
 }

-- 
In theory, practice and theory are the same, but in practice they 
are different -- Larry McVoy
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