[RFC PATCH -v2] ext4: Switch to non delalloc mode when we are low on free blocks count.

Aneesh Kumar K.V
2008-08-25T11:20:42Z

delayed allocation allocate blocks during writepages. That also
means we cannot handle block allocation failures. Switch to
non - delalloc when we are running low on free blocks.
Delayed allocation need to do aggressive meta-data block reservation
considering that the requested blocks can all be discontiguous.
Switching to non-delalloc avoids that. Also we can satisfy
partial write in non-delalloc mode.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
fs/ext4/inode.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
1 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3f3ecc0..d923a14 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2482,6 +2482,29 @@ static int ext4_da_writepages(struct address_space *mapping,
return ret;
}

+#define FALL_BACK_TO_NONDELALLOC 1
+static int ext4_nonda_switch(struct super_block *sb)
+{
+ s64 free_blocks, dirty_blocks;
+ struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+ /*
+ * switch to non delalloc mode if we are running low
+ * on free block. The free block accounting via percpu
+ * counters can get slightly wrong with FBC_BATCH getting
+ * accumulated on each CPU without updating global counters
+ * Delalloc need an accurate free block accounting. So switch
+ * to non delalloc when we are near to error range.
+ */
+ free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
+ dirty_blocks = percpu_counter_read_positive(&sbi->s_dirtyblocks_counter);
+ if ( 2 * free_blocks < 3 * dirty_blocks) {
+ /* free block count is less that 150% of dirty blocks */
+ return 1;
+ }
+ return 0;
+}
+
static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
@@ -2496,6 +2519,13 @@ static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
index = pos >> PAGE_CACHE_SHIFT;
from = pos & (PAGE_CACHE_SIZE - 1);
to = from + len;
+
+ if (ext4_nonda_switch(inode->i_sb)) {
+ *fsdata = (void *)FALL_BACK_TO_NONDELALLOC;
+ return ext4_write_begin(file, mapping, pos,
+ len, flags, pagep, fsdata);
+ }
+ *fsdata = (void *)0;
retry:
/*
* With delayed allocation, we don't log the i_disksize update
@@ -2564,6 +2594,19 @@ static int ext4_da_write_end(struct file *file,
handle_t *handle = ext4_journal_current_handle();
loff_t new_i_size;
unsigned long start, end;
+ int write_mode = (int)fsdata;
+
+ if (write_mode == FALL_BACK_TO_NONDELALLOC) {
+ if (ext4_should_order_data(inode)) {
+ return ext4_ordered_write_end(file, mapping, pos,
+ len, copied, page, fsdata);
+ } else if (ext4_should_writeback_data(inode)) {
+ return ext4_writeback_write_end(file, mapping, pos,
+ len, copied, page, fsdata);
+ } else {
+ BUG();
+ }
+ }

start = pos & (PAGE_CACHE_SIZE - 1);
end = start + copied -1;
@@ -4901,6 +4944,7 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
loff_t size;
unsigned long len;
int ret = -EINVAL;
+ void *fsdata;
struct file *file = vma->vm_file;
struct inode *inode = file->f_path.dentry->d_inode;
struct address_space *mapping = inode->i_mapping;
@@ -4939,11 +4983,11 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
* on the same page though
*/
ret = mapping->a_ops->write_begin(file, mapping, page_offset(page),
- len, AOP_FLAG_UNINTERRUPTIBLE, &page, NULL);
+ len, AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
if (ret < 0)
goto out_unlock;
ret = mapping->a_ops->write_end(file, mapping, page_offset(page),
- len, len, page, NULL);
+ len, len, page, fsdata);
if (ret < 0)
goto out_unlock;
ret = 0;
--
1.6.0.1.90.g27a6e