do_generic_file_read / readahead adjustments

PATCH New [email protected] 1 participant 1 message Oct 16, 2002

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2002-10-16 18:01 UTC #0 lore raw

PATCH 1/1 do_generic_file_read / readahead adjustments

Hi Linus,

The attached patch does the following three things:

(1) Makes the functions in mm/readahead.c only use struct file* to pass to readpage(). address_mapping* and file_ra_state* are used instead to keep track of readahead stuff.

(2) Adds a new function do_generic_mapping_read() that is similar to do_generic_file_read(), except that it uses a mapping pointer and a readahead state pointer to access a file. The file* is only used to pass to readpage().

(3) Turns do_generic_file_read() into an inline function in linux/fs.h that simply wraps do_generic_mapping_read().

This should mean that it is no longer necessary to have a struct file to access a file in this manner. Just an inode or address space should be sufficient.

It also means alternate read-ahead structures can be maintained.

The reason I want this is that I'm writing a general cache manager for filesystems such as AFS, NFSv4, and Lustre. Block devices are made available to the "cache manager" by means of a filesystem that can be mounted. I'm storing meta data in an inode in the cache, but to scan this at the moment I need to gain a "struct file" to use with do_generic_file_read().

This involves either creating a dummy dentry and struct file (which will cause Al Viro to come looking for me with a shotgun), or to use an extra auxilliary filesystem mounted with do_kern_mount(), neither of which are particularly appealing.

This patch is the alternative... it provides a function that I can pass an address_space to. This also allows me to make use of readahead semantics without having to reinvent them for myself.

Quoted 9 lines · Rik van Riel

Quoted 5 lines · Andrew Morton
Quoted 2 lines · David Howells
The attached patch does the following three things:
Seems sensible. Is there something out there which actually uses this?
I think David has a few things up his sleeve. The patch looks sensible.

Are you willing to take this from me directly, or do I need to pass it via someone else?

David

include/linux/fs.h +14 -1

diff -u -x '*.o' -x '*.cmd' -x '*~' linux-2.5.43/include/linux/fs.h linux-readahead-2543/include/linux/fs.h
@@ -1251,7 +1251,8 @@
 ssize_t generic_file_write_nolock(struct file *file, const struct iovec *iov,
 				unsigned long nr_segs, loff_t *ppos);
 extern ssize_t generic_file_sendfile(struct file *, struct file *, loff_t *, size_t);
-extern void do_generic_file_read(struct file *, loff_t *, read_descriptor_t *, read_actor_t);
+extern void do_generic_mapping_read(struct address_space *, struct file_ra_state *, struct file *,
+				    loff_t *, read_descriptor_t *, read_actor_t);
 extern ssize_t generic_file_direct_IO(int rw, struct file *file,
 	const struct iovec *iov, loff_t offset, unsigned long nr_segs);
 extern int generic_direct_IO(int rw, struct inode *inode, const struct iovec

@@ -1268,6 +1269,18 @@
 extern int generic_vm_writeback(struct page *page,
 				struct writeback_control *wbc);
 
+static inline void do_generic_file_read(struct file * filp, loff_t *ppos,
+					read_descriptor_t * desc,
+					read_actor_t actor)
+{
+	do_generic_mapping_read(filp->f_dentry->d_inode->i_mapping,
+				&filp->f_ra,
+				filp,
+				ppos,
+				desc,
+				actor);
+}
+
 extern struct file_operations generic_ro_fops;
 
 extern int vfs_readlink(struct dentry *, char *, int, const char *);

include/linux/mm.h +11 -4

diff -u -x '*.o' -x '*.cmd' -x '*~' linux-2.5.43/include/linux/mm.h linux-readahead-2543/include/linux/mm.h
@@ -513,11 +513,18 @@
 /* readahead.c */
 #define VM_MAX_READAHEAD	128	/* kbytes */
 #define VM_MIN_READAHEAD	16	/* kbytes (includes current page) */
-int do_page_cache_readahead(struct file *file,
+int do_page_cache_readahead(struct address_space *mapping, struct file *filp,
 			unsigned long offset, unsigned long nr_to_read);
-void page_cache_readahead(struct file *file, unsigned long offset);
-void page_cache_readaround(struct file *file, unsigned long offset);
-void handle_ra_miss(struct file *file);
+void page_cache_readahead(struct address_space *mapping, 
+			  struct file_ra_state *ra,
+			  struct file *filp,
+			  unsigned long offset);
+void page_cache_readaround(struct address_space *mapping, 
+			   struct file_ra_state *ra,
+			   struct file *filp,
+			   unsigned long offset);
+void handle_ra_miss(struct address_space *mapping, 
+		    struct file_ra_state *ra);
 
 /* Do stack extension */
 extern int expand_stack(struct vm_area_struct * vma, unsigned long address);

kernel/ksyms.c +1 -1

diff -ur -x '*.o' -x '*.cmd' -x '*~' linux-2.5.43/kernel/ksyms.c linux-readahead-2543/kernel/ksyms.c
@@ -229,7 +229,7 @@
 EXPORT_SYMBOL(generic_block_bmap);
 EXPORT_SYMBOL(generic_file_read);
 EXPORT_SYMBOL(generic_file_sendfile);
-EXPORT_SYMBOL(do_generic_file_read);
+EXPORT_SYMBOL(do_generic_mapping_read);
 EXPORT_SYMBOL(generic_file_write);
 EXPORT_SYMBOL(generic_file_write_nolock);
 EXPORT_SYMBOL(generic_file_mmap);

mm/filemap.c +17 ~~-11~~

diff -ur -x '*.o' -x '*.cmd' -x '*~' linux-2.5.43/mm/filemap.c linux-readahead-2543/mm/filemap.c
@@ -572,10 +572,14 @@
  * This is really ugly. But the goto's actually try to clarify some
  * of the logic when it comes to error handling etc.
  * - note the struct file * is only passed for the use of readpage
  */
-void do_generic_file_read(struct file * filp, loff_t *ppos, read_descriptor_t * desc, read_actor_t actor)
+void do_generic_mapping_read(struct address_space *mapping,
+			     struct file_ra_state *ra,
+			     struct file * filp,
+			     loff_t *ppos,
+			     read_descriptor_t * desc,
+			     read_actor_t actor)
 {
-	struct address_space *mapping = filp->f_dentry->d_inode->i_mapping;
 	struct inode *inode = mapping->host;
 	unsigned long index, offset;
 	struct page *cached_page;

@@ -599,7 +603,7 @@
 				break;
 		}
 
-		page_cache_readahead(filp, index);
+		page_cache_readahead(mapping, ra, filp, index);
 
 		nr = nr - offset;

@@ -611,7 +615,7 @@
 		page = radix_tree_lookup(&mapping->page_tree, index);
 		if (!page) {
 			read_unlock(&mapping->page_lock);
-			handle_ra_miss(filp);
+			handle_ra_miss(mapping,ra);
 			goto no_cached_page;
 		}
 		page_cache_get(page);

@@ -947,9 +951,9 @@
 }
 
 static ssize_t
-do_readahead(struct file *file, unsigned long index, unsigned long nr)
+do_readahead(struct address_space *mapping, struct file *filp,
+	     unsigned long index, unsigned long nr)
 {
-	struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
 	unsigned long max;
 	unsigned long active;
 	unsigned long inactive;

@@ -963,7 +967,7 @@
 	if (nr > max)
 		nr = max;
 
-	do_page_cache_readahead(file, index, nr);
+	do_page_cache_readahead(mapping, filp, index, nr);
 	return 0;
 }

@@ -976,10 +980,11 @@
 	file = fget(fd);
 	if (file) {
 		if (file->f_mode & FMODE_READ) {
+			struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
 			unsigned long start = offset >> PAGE_CACHE_SHIFT;
 			unsigned long end = (offset + count - 1) >> PAGE_CACHE_SHIFT;
 			unsigned long len = end - start + 1;
-			ret = do_readahead(file, start, len);
+			ret = do_readahead(mapping, file, start, len);
 		}
 		fput(file);
 	}

@@ -1000,6 +1005,7 @@
 	int error;
 	struct file *file = area->vm_file;
 	struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
+	struct file_ra_state *ra = &file->f_ra;
 	struct inode *inode = mapping->host;
 	struct page *page;
 	unsigned long size, pgoff, endoff;

@@ -1032,7 +1038,7 @@
 	 */
 	if (VM_SequentialReadHint(area)) {
 		did_readahead = 1;
-		page_cache_readahead(area->vm_file, pgoff);
+		page_cache_readahead(mapping, ra, file, pgoff);
 	}
 
 	/*

@@ -1041,7 +1047,7 @@
 	 */
 	if ((pgoff < size) && !VM_RandomReadHint(area)) {
 		did_readahead = 1;
-		page_cache_readaround(file, pgoff);
+		page_cache_readaround(mapping, ra, file, pgoff);
 	}
 
 	/*

@@ -1051,7 +1057,7 @@
 	page = find_get_page(mapping, pgoff);
 	if (!page) {
 		if (did_readahead) {
-			handle_ra_miss(file);
+			handle_ra_miss(mapping,ra);
 			did_readahead = 0;
 		}
 		goto no_cached_page;

mm/madvise.c +1 -1

diff -ur -x '*.o' -x '*.cmd' -x '*~' linux-2.5.43/mm/madvise.c linux-readahead-2543/mm/madvise.c
@@ -80,7 +80,7 @@
 	if ((vma->vm_mm->rss + (end - start)) > rlim_rss)
 		return error;
 
-	do_page_cache_readahead(file, start, end - start);
+	do_page_cache_readahead(file->f_dentry->d_inode->i_mapping, file, start, end - start);
 	return 0;
 }

mm/readahead.c +23 ~~-23~~

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