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Message-ID: <20130215071245.GE26945@gmail.com>
Date: Fri, 15 Feb 2013 15:12:45 +0800
From: Zheng Liu <gnehzuil.liu@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>,
Theodore Ts'o <tytso@....edu>
Subject: Re: [PATCH 09/10 v5] ext4: convert unwritten extents from extent
status tree in end_io
On Tue, Feb 12, 2013 at 01:51:59PM +0100, Jan Kara wrote:
> On Fri 08-02-13 16:44:05, Zheng Liu wrote:
> > From: Zheng Liu <wenqing.lz@...bao.com>
> >
> > This commit tries to convert unwritten extents from extent status tree
> > in end_io callback functions and ext4_ext_direct_IO.
> Why should we do this?
>
> ...
> > @@ -801,3 +807,147 @@ static int __es_try_to_reclaim_extents(struct ext4_inode_info *ei,
> > tree->cache_es = NULL;
> > return nr_shrunk;
> > }
> > +
> > +int ext4_es_convert_unwritten_extents(struct inode *inode, loff_t offset,
> > + size_t size)
> > +{
> > + struct ext4_es_tree *tree;
> > + struct rb_node *node;
> > + struct extent_status *es, orig_es, conv_es;
> > + ext4_lblk_t end, len1, len2;
> > + ext4_lblk_t lblk = 0, len = 0;
> > + ext4_fsblk_t block;
> > + unsigned long flags;
> > + unsigned int blkbits;
> > + int err = 0;
> > +
> > + trace_ext4_es_convert_unwritten_extents(inode, offset, size);
> > + blkbits = inode->i_blkbits;
> > + lblk = offset >> blkbits;
> > + len = (EXT4_BLOCK_ALIGN(offset + size, blkbits) >> blkbits) - lblk;
> > +
> > + end = lblk + len - 1;
> > + BUG_ON(end < lblk);
> > +
> > + tree = &EXT4_I(inode)->i_es_tree;
> > +
> > + write_lock_irqsave(&EXT4_I(inode)->i_es_lock, flags);
> > + es = __es_tree_search(&tree->root, lblk);
> > + if (!es)
> > + goto out;
> > + if (es->es_lblk > end)
> > + goto out;
> > +
> > + tree->cache_es = NULL;
> > +
> > + orig_es.es_lblk = es->es_lblk;
> > + orig_es.es_len = es->es_len;
> > + orig_es.es_pblk = es->es_pblk;
> > +
> > + len1 = lblk > es->es_lblk ? lblk - es->es_lblk : 0;
> > + len2 = ext4_es_end(es) > end ?
> > + ext4_es_end(es) - end : 0;
> > + if (len1 > 0)
> > + es->es_len = len1;
> > + if (len2 > 0) {
> > + if (len1 > 0) {
> > + struct extent_status newes;
> > +
> > + newes.es_lblk = end + 1;
> > + newes.es_len = len2;
> > + block = ext4_es_pblock(&orig_es) +
> > + orig_es.es_len - len2;
> > + ext4_es_store_pblock(&newes, block);
> > + ext4_es_store_status(&newes, ext4_es_status(&orig_es));
> > + err = __es_insert_extent(inode, &newes);
> > + if (err) {
> > + es->es_lblk = orig_es.es_lblk;
> > + es->es_len = orig_es.es_len;
> > + es->es_pblk = orig_es.es_pblk;
> > + goto out;
> > + }
> > +
> > + conv_es.es_lblk = orig_es.es_lblk + len1;
> > + conv_es.es_len = orig_es.es_len - len1 - len2;
> > + block = ext4_es_pblock(&orig_es) + len1;
> > + ext4_es_store_pblock(&conv_es, block);
> > + ext4_es_store_status(&conv_es, EXTENT_STATUS_WRITTEN);
> > + err = __es_insert_extent(inode, &conv_es);
> > + if (err) {
> > + int err2 = __es_remove_extent(inode,
> > + conv_es.es_lblk,
> > + ext4_es_end(&newes));
> > + if (err2)
> > + goto out;
> > + es->es_lblk = orig_es.es_lblk;
> > + es->es_len = orig_es.es_len;
> > + es->es_pblk = orig_es.es_pblk;
> > + goto out;
> > + }
> > + } else {
> > + es->es_lblk = end + 1;
> > + es->es_len = len2;
> > + block = ext4_es_pblock(&orig_es) +
> > + orig_es.es_len - len2;
> > + ext4_es_store_pblock(es, block);
> > +
> > + conv_es.es_lblk = orig_es.es_lblk;
> > + conv_es.es_len = orig_es.es_len - len2;
> > + ext4_es_store_pblock(&conv_es,
> > + ext4_es_pblock(&orig_es));
> > + ext4_es_store_status(&conv_es, EXTENT_STATUS_WRITTEN);
> > + err = __es_insert_extent(inode, &conv_es);
> > + if (err) {
> > + es->es_lblk = orig_es.es_lblk;
> > + es->es_len = orig_es.es_len;
> > + es->es_pblk = orig_es.es_pblk;
> > + }
> > + }
> > + goto out;
> > + }
> > +
> > + if (len1 > 0) {
> > + node = rb_next(&es->rb_node);
> > + if (node)
> > + es = rb_entry(node, struct extent_status, rb_node);
> > + else
> > + es = NULL;
> > + }
> > +
> > + while (es && ext4_es_end(es) <= end) {
> > + node = rb_next(&es->rb_node);
> > + ext4_es_store_status(es, EXTENT_STATUS_WRITTEN);
> > + if (!inode) {
> > + es = NULL;
> > + break;
> > + }
> > + es = rb_entry(node, struct extent_status, rb_node);
> > + }
> > +
> > + if (es && es->es_lblk < end + 1) {
> > + ext4_lblk_t orig_len = es->es_len;
> > +
> > + /*
> > + * Here we first set conv_es just because of avoiding copy the
> > + * value of es to a temporary variable.
> > + */
> > + len1 = ext4_es_end(es) - end;
> > + conv_es.es_lblk = es->es_lblk;
> > + conv_es.es_len = es->es_len - len1;
> > + ext4_es_store_pblock(&conv_es, ext4_es_pblock(es));
> > + ext4_es_store_status(&conv_es, EXTENT_STATUS_WRITTEN);
> > +
> > + es->es_lblk = end + 1;
> > + es->es_len = len1;
> > + block = ext4_es_pblock(es) + orig_len - len1;
> > + ext4_es_store_pblock(es, block);
> > +
> > + err = __es_insert_extent(inode, &conv_es);
> > + if (err)
> > + goto out;
> > + }
> > +
> > +out:
> > + write_unlock_irqrestore(&EXT4_I(inode)->i_es_lock, flags);
> > + return err;
> > +}
> Is this really needed? Why don't you just use ext4_es_insert_extent() to
> insert new extent of proper type? Also the way you wrote it, we can return
> (freshly written) data to the user, then reclaim the extent status from
> memory and later return 0s because we read the original status from disk
> (conversion hasn't still happened on disk). That would be certainly
> confusing.
Yes, you are right. So it seems that a new flag called
EXTENT_STATUS_DIRTY need to be defined to prevent memory reclaim from
shrinker.
Thanks,
- Zheng
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