o_streaming.patch

patches for linux-2.6.

This patch by Robert Love prevents files opened as O_STREAMING from
consuming disk cache pages prior to the current file pointer. It has 
been ported to kernel 2.6 using the infrastructure of posix_fadvice 
system call which is now the default interface for achieving this kind
of operation.

--- linux26-cvs/include/asm-mips/fcntl.h	Wed Mar  9 11:21:27 2005
+++ linux26-tony/include/asm-mips/fcntl.h	Tue Jun 28 13:48:26 2005
@@ -27,6 +27,7 @@
 #define O_DIRECTORY	0x10000	/* must be a directory */
 #define O_NOFOLLOW	0x20000	/* don't follow links */
 #define O_NOATIME	0x40000
+#define O_STREAMING	0x400000	/* streaming access */
 
 #define O_NDELAY	O_NONBLOCK
 
--- linux26-cvs/mm/filemap.c	Wed Mar  9 11:38:28 2005
+++ linux26-tony/mm/filemap.c	Tue Jun 28 13:36:12 2005
@@ -669,6 +669,32 @@
 
 EXPORT_SYMBOL(grab_cache_page_nowait);
 
+/**
+ * shrink_pagecache - nonblockingly drop pages from the mapping.
+ * @file: the file we are doing I/O on
+ * @max_index: the maximum index from which we are willing to drop pages
+ * 
+ * This is for O_STREAMING, which says "I am streaming data, I know I will not
+ * revisit this; do not cache anything".
+ * 
+ * max_index allows us to only drop pages which are behind `index', to avoid
+ * trashing readahead.
+ */
+static unsigned long shrink_pagecache(struct file *file,
+				      unsigned long max_index)
+{
+	struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
+	
+	/*
+	* ensure we have a decent amount of work todo
+	*/
+	if (mapping->nrpages < 256)
+		return 0;
+
+	invalidate_mapping_pages(mapping, 0, max_index);
+	return 0;
+}
+
 /*
  * This is a generic file read routine, and uses the
  * mapping->a_ops->readpage() function for the actual low-level
@@ -886,6 +912,8 @@
 	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
 	if (cached_page)
 		page_cache_release(cached_page);
+	if (filp->f_flags & O_STREAMING)
+		shrink_pagecache(filp, index);
 	if (filp)
 		file_accessed(filp);
 }
@@ -1940,7 +1968,10 @@
 		filemap_set_next_iovec(&cur_iov, &iov_base, written);
 		buf = iov->iov_base + iov_base;
 	}
-
+	
+	if (file->f_flags & O_STREAMING)
+		shrink_pagecache(file, pos >> PAGE_CACHE_SHIFT);
+	
 	do {
 		unsigned long index;
 		unsigned long offset;