On Tue, 2008-04-15 at 16:28 -0700, Mingming Cao wrote:
> On Tue, 2008-04-15 at 11:08 -0700, Mingming Cao wrote:
> > On Tue, 2008-04-15 at 18:14 +0200, Jan Kara wrote:
> > > Hi,
> > >
> > > I've ported my patch inversing locking ordering of page_lock and
> > > transaction start to ext4 (on top of ext4 patch queue). Everything except
> > > delayed allocation is converted (the patch is below for interested
> > > readers). The question is how to proceed with delayed allocation. Its
> > > current implementation in VFS is designed to work well with the old
> > > ordering (page lock first, then start a transaction). We could bend it to
> > > work with the new locking ordering but I really see no point since ext4 is
> > > the only user.
> >
> > I think the plan is port the changes to ext2/3/JFS and support delayed
> > allocation on those filesystems.
> >
> > > Also XFS has AFAIK ordering first start transaction, then
> > > lock pages so if we should ever merge delayed alloc implementations the new
> > > ordering would make it easier.
> > > So what do people think here? Do you agree with reimplementing current
> > > mpage_da_... functions?
> >
> > It worth a try, but I could not see how to bend delayed allocation to
> > work the new ordering:( With delayed allocation Ext4 gets into
> > writepage() directly with page locked, but we need to start transaction
> > to do block allocation...:(
>
> Looked again it seems possible to reservse the order with delayed
> allocation. with ext3_da_writepgaes() we could start the journal before
> calling mpage_da_writepages()(which will lock the pages), instead of
> start the journal inside ext4_da_get_block_write(). So that we could get
> the locking order right. Just need to taking care of the estimated
> credits right.
>
> How about this? (untested, just throw out for comment)
Seems sent out an old version, this version compiles
---
fs/ext4/inode.c | 53 ++++++++++++++++++++++++++++++++++++++++-------------
1 file changed, 40 insertions(+), 13 deletions(-)
Index: linux-2.6.25-rc9/fs/ext4/inode.c
===================================================================
--- linux-2.6.25-rc9.orig/fs/ext4/inode.c 2008-04-15 15:40:33.000000000 -0700
+++ linux-2.6.25-rc9/fs/ext4/inode.c 2008-04-15 16:32:10.000000000 -0700
@@ -1437,18 +1437,12 @@ static int ext4_da_get_block_prep(struct
static int ext4_da_get_block_write(struct inode *inode, sector_t iblock,
struct buffer_head *bh_result, int create)
{
- int ret, needed_blocks = ext4_writepage_trans_blocks(inode);
+ int ret;
unsigned max_blocks = bh_result->b_size >> inode->i_blkbits;
loff_t disksize = EXT4_I(inode)->i_disksize;
handle_t *handle = NULL;
- if (create) {
- handle = ext4_journal_start(inode, needed_blocks);
- if (IS_ERR(handle)) {
- ret = PTR_ERR(handle);
- goto out;
- }
- }
+ handle = ext4_journal_current_handle();
ret = ext4_get_blocks_wrap(handle, inode, iblock, max_blocks,
bh_result, create, 0);
@@ -1483,17 +1477,51 @@ static int ext4_da_get_block_write(struc
ret = 0;
}
-out:
- if (handle && !IS_ERR(handle))
- ext4_journal_stop(handle);
-
return ret;
}
+/*
+ * For now just follow the DIO way to estimate the max credits
+ * needed to write out EXT4_MAX_BUF_BLOCKS pages.
+ * todo: need to calculate the max credits need for
+ * extent based files, currently the DIO credits is based on
+ * indirect-blocks mapping way.
+ *
+ * Probably should have a generic way to calculate credits
+ * for DIO, writepages, and truncate
+ */
+#define EXT4_MAX_BUF_BLOCKS DIO_MAX_BLOCKS
+#define EXT4_MAX_BUF_CREDITS DIO_CREDITS
+
static int ext4_da_writepages(struct address_space *mapping,
struct writeback_control *wbc)
{
- return mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
+ struct inode *inode = mapping->host;
+ handle_t *handle = NULL;
+ int needed_blocks;
+ int ret;
+
+ /*
+ * Estimate the worse case needed credits to write out
+ * EXT4_MAX_BUF_BLOCKS pages
+ */
+ needed_blocks = EXT4_MAX_BUF_CREDITS;
+
+ /* start the transaction with credits*/
+ handle = ext4_journal_start(inode, needed_blocks);
+ if (IS_ERR(handle)) {
+ ret = PTR_ERR(handle);
+ return ret;
+ }
+
+ /* set the max pages could be write-out at a time */
+ wbc->range_end = wbc->range_start +
+ EXT4_MAX_BUF_BLOCKS << PAGE_CACHE_SHIFT - 1;
+
+ ret = mpage_da_writepages(mapping, wbc, ext4_da_get_block_write);
+ ext4_journal_stop(handle);
+
+ return ret;
}
static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
--
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