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SubjectRe: PATCH: killing read_ahead[]


On Wed, 25 Oct 2000, Alexander Viro wrote:

> I can do the proof-of-concept patch (below 10Kb, ext2 + generic code, with
> the need to repeat the fs-specific parts for other filesystems) in an
> hour. Clearance?

OK, it didn't take an hour. Warning: completely untested, needs
(trivial) changes to other filesystems.

Rules: when you change i_size for inode with non-trivial ->a_ops -
either call update_cached_size(inode) or do the equivalent by hands
(e.g. generic_commit_write have to mess with i_size value to update the
->size_in_pages and ->last_page_size - we already have them calculated).
Ditto for the places where you set ->a_ops.

Invariants:
inode->i_mapping->size_in_pages ==
(inode->i_size + PAGE_CACHE_SIZE - 1)>>PAGE_CACHE_SHIFT;
inode->i_size == ((....->size_in_pages-1)<<PAGE_CACHE_SHIFT) +
....->last_page_size;
Linus, what do you think about that? I can do the remaining filesystems
and give it initial testing today.

diff -urN rc10-pre5/fs/buffer.c rc10-pre5-size_in_pages/fs/buffer.c
--- rc10-pre5/fs/buffer.c Tue Oct 24 01:27:28 2000
+++ rc10-pre5-size_in_pages/fs/buffer.c Wed Oct 25 17:46:25 2000
@@ -1751,6 +1751,9 @@
kunmap(page);
if (pos > inode->i_size) {
inode->i_size = pos;
+ /* to is always positive */
+ page->mapping->size_in_pages = page->index+1;
+ page->mapping->last_page_size = to;
mark_inode_dirty(inode);
}
return 0;
@@ -1835,19 +1838,22 @@
int block_write_full_page(struct page *page, get_block_t *get_block)
{
struct inode *inode = (struct inode*)page->mapping->host;
- unsigned long end_index = inode->i_size >> PAGE_CACHE_SHIFT;
+ unsigned long end_index = page->mapping->size_in_pages;
unsigned offset;
int err;

/* easy case */
- if (page->index < end_index)
- return __block_write_full_page(inode, page, get_block);
-
- /* things got complicated... */
- offset = inode->i_size & (PAGE_CACHE_SIZE-1);
+ if (page->index+1 < end_index)
+ goto easy;
/* OK, are we completely out? */
- if (page->index >= end_index+1 || !offset)
+ if (page->index+1 > end_index)
return -EIO;
+
+ offset = inode->i_mapping->last_page_size;
+ /* Another easy case - 'partial' page is not */
+ if (offset == PAGE_CACHE_SIZE)
+ goto easy;
+
/* Sigh... will have to work, then... */
err = __block_prepare_write(inode, page, 0, offset, get_block);
if (!err) {
@@ -1860,6 +1866,8 @@
}
ClearPageUptodate(page);
goto done;
+easy:
+ return __block_write_full_page(inode, page, get_block);
}

int generic_block_bmap(struct address_space *mapping, long block, get_block_t *get_block)
diff -urN rc10-pre5/fs/ext2/inode.c rc10-pre5-size_in_pages/fs/ext2/inode.c
--- rc10-pre5/fs/ext2/inode.c Wed Oct 4 03:44:54 2000
+++ rc10-pre5-size_in_pages/fs/ext2/inode.c Wed Oct 25 17:41:24 2000
@@ -54,6 +54,8 @@
mark_inode_dirty(inode);
ext2_update_inode(inode, IS_SYNC(inode));
inode->i_size = 0;
+ inode.i_data->size_in_pages = 0;
+ inode.i_data->last_page_size = PAGE_CACHE_SIZE;
if (inode->i_blocks)
ext2_truncate (inode);
ext2_free_inode (inode);
@@ -1063,6 +1065,7 @@
inode->i_op = &ext2_file_inode_operations;
inode->i_fop = &ext2_file_operations;
inode->i_mapping->a_ops = &ext2_aops;
+ update_cached_size(inode);
} else if (S_ISDIR(inode->i_mode)) {
inode->i_op = &ext2_dir_inode_operations;
inode->i_fop = &ext2_dir_operations;
@@ -1072,6 +1075,7 @@
else {
inode->i_op = &page_symlink_inode_operations;
inode->i_mapping->a_ops = &ext2_aops;
+ update_cached_size(inode);
}
} else
init_special_inode(inode, inode->i_mode,
diff -urN rc10-pre5/fs/inode.c rc10-pre5-size_in_pages/fs/inode.c
--- rc10-pre5/fs/inode.c Tue Oct 24 01:27:29 2000
+++ rc10-pre5-size_in_pages/fs/inode.c Wed Oct 25 17:39:28 2000
@@ -529,6 +529,8 @@
inode->i_bdev = NULL;
inode->i_data.a_ops = &empty_aops;
inode->i_data.host = (void*)inode;
+ inode->i_data.size_in_pages = 0;
+ inode->i_data.last_page_size = PAGE_CACHE_SIZE;
inode->i_mapping = &inode->i_data;
}

diff -urN rc10-pre5/include/linux/fs.h rc10-pre5-size_in_pages/include/linux/fs.h
--- rc10-pre5/include/linux/fs.h Tue Oct 24 01:27:36 2000
+++ rc10-pre5-size_in_pages/include/linux/fs.h Wed Oct 25 17:31:40 2000
@@ -366,6 +366,8 @@
struct vm_area_struct *i_mmap; /* list of private mappings */
struct vm_area_struct *i_mmap_shared; /* list of shared mappings */
spinlock_t i_shared_lock; /* and spinlock protecting it */
+ unsigned long size_in_pages;
+ unsigned last_page_size;
};

struct block_device {
@@ -456,6 +458,16 @@
#define I_LOCK 2
#define I_FREEING 4
#define I_CLEAR 8
+
+static inline void update_cached_size(struct inode *inode)
+{
+ loff_t size = inode->i_size;
+ inode->i_mapping.size_in_pages =
+ (size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+ if ((size &= ~PAGE_CACHE_MASK) == 0)
+ size = PAGE_CACHE_SIZE;
+ inode->i_mapping.last_page_size = size;
+}

extern void __mark_inode_dirty(struct inode *);
static inline void mark_inode_dirty(struct inode *inode)
diff -urN rc10-pre5/mm/filemap.c rc10-pre5-size_in_pages/mm/filemap.c
--- rc10-pre5/mm/filemap.c Tue Oct 24 01:27:38 2000
+++ rc10-pre5-size_in_pages/mm/filemap.c Wed Oct 25 17:43:01 2000
@@ -429,8 +429,7 @@
*/
static inline int page_cache_read(struct file * file, unsigned long offset)
{
- struct inode *inode = file->f_dentry->d_inode;
- struct address_space *mapping = inode->i_mapping;
+ struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
struct page **hash = page_hash(mapping, offset);
struct page *page;

@@ -633,8 +632,7 @@
*/
static void drop_behind(struct file * file, unsigned long index)
{
- struct inode *inode = file->f_dentry->d_inode;
- struct address_space *mapping = inode->i_mapping;
+ struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
struct page **hash;
struct page *page;
unsigned long start;
@@ -794,7 +792,7 @@
struct file * filp, struct inode * inode,
struct page * page)
{
- unsigned long end_index = inode->i_size >> PAGE_CACHE_SHIFT;
+ unsigned long end_index = inode->i_mapping->size_in_pages;
unsigned long index = page->index;
unsigned long max_ahead, ahead;
unsigned long raend;
@@ -819,8 +817,8 @@
filp->f_rawin = 0;
filp->f_ralen = 1;
if (!max_ahead) {
- filp->f_raend = index + filp->f_ralen;
- filp->f_rawin += filp->f_ralen;
+ filp->f_raend = index + 1;
+ filp->f_rawin = 1;
}
}
}
@@ -966,14 +964,14 @@

for (;;) {
struct page *page, **hash;
- unsigned long end_index, nr;
+ unsigned nr;

- end_index = inode->i_size >> PAGE_CACHE_SHIFT;
- if (index > end_index)
+ if (index >= mapping->size_in_pages)
break;
+
nr = PAGE_CACHE_SIZE;
- if (index == end_index) {
- nr = inode->i_size & ~PAGE_CACHE_MASK;
+ if (index == mapping->size_in_pages - 1) {
+ nr = mapping->last_page_size;
if (nr <= offset)
break;
}
@@ -1328,10 +1326,9 @@
{
int error;
struct file *file = area->vm_file;
- struct inode *inode = file->f_dentry->d_inode;
- struct address_space *mapping = inode->i_mapping;
+ struct address_space *mapping = file->f_dentry->d_inode->i_mapping;
struct page *page, **hash, *old_page;
- unsigned long size = (inode->i_size + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
+ unsigned long size = mapping->size_in_pages;

unsigned long pgoff = ((address - area->vm_start) >> PAGE_CACHE_SHIFT) + area->vm_pgoff;

@@ -1910,8 +1907,7 @@
if (!vma->vm_file)
return error;
file = vma->vm_file;
- size = (file->f_dentry->d_inode->i_size + PAGE_CACHE_SIZE - 1) >>
- PAGE_CACHE_SHIFT;
+ size = file->f_dentry->d_inode->i_mapping->size_in_pages;

start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
if (end > vma->vm_end)
diff -urN rc10-pre5/mm/memory.c rc10-pre5-size_in_pages/mm/memory.c
--- rc10-pre5/mm/memory.c Tue Oct 24 01:27:38 2000
+++ rc10-pre5-size_in_pages/mm/memory.c Wed Oct 25 17:44:14 2000
@@ -979,6 +979,7 @@
if (inode->i_size < offset)
goto do_expand;
inode->i_size = offset;
+ update_cached_size(inode);
truncate_inode_pages(mapping, offset);
spin_lock(&mapping->i_shared_lock);
if (!mapping->i_mmap && !mapping->i_mmap_shared)
@@ -1013,6 +1014,7 @@
}
}
inode->i_size = offset;
+ update_cached_size(inode);
if (inode->i_op && inode->i_op->truncate)
inode->i_op->truncate(inode);
out:
-
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