Hi Lukas,

On Mon, Jul 23, 2012 at 01:01:53PM +0200, Lukáš Czerner wrote:

On Sun, 22 Jul 2012, Zheng Liu wrote:

quoted

Date: Sun, 22 Jul 2012 15:59:45 +0800
From: Zheng Liu <redacted>
To: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Cc: xiaoqiangnk@gmail.com, achender@linux.vnet.ibm.com, wenqing.lz@taobao.com
Subject: [RFC][PATCH 09/10 v1][RESEND] ext4: don't need to writeout all dirty
    pages in punch hole

From: Zheng Liu <redacted>

Now we don't need to writeout all dirty pages when punching a hole.  The i_mutex
locking is taken to avoid concurrent writes.  In truncate_pagecache_range, all
pages in this hole is released, and ext4_es_remove_space is called to update
extent status tree. 

Hi Zheng,

I am currently in the middle of reworking punch hole for ext4 so
there will be some changes in this area. See the patch set

http://www.spinics.net/lists/linux-ext4/msg33014.html

Thank you for your reminding.  I have seen your patch set and it is
pretty cool.  IMHO your patch set shall be merged into upstream kernel
before applying io tree because io tree still has a lot of things that
needs to be done.  So I will change it according to your patches. :-)

Moreover I think that we should avoid taking i_mutex if we can and I
believe that we can in this case, because we only need to prevent
allocation. So I just want to let you know that this part is
probably going to change anyway.

It seems that we need to take i_mutex locking to prevent from buffered
writes after page cache has been truncated by truncate_pagecache_range.
If a buffered write without delalloc occurs after truncating page cache
and before taking i_data_sem, that means that the allocated block for
this buffered write will be removed in ext4_ext_remove_space when the
offset is within the range of the hole.  Am I missing something?

Regards,
Zheng

quoted

Signed-off-by: Zheng Liu <redacted>
---
 fs/ext4/extents.c |   28 ++++++++++++----------------
 1 files changed, 12 insertions(+), 16 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index f2c5294..2a526b4 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c

@@ -4529,9 +4529,11 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
 	loff_t first_page_offset, last_page_offset;
 	int credits, err = 0;
 
+	mutex_lock(&inode->i_mutex);
+
 	/* No need to punch hole beyond i_size */
 	if (offset >= inode->i_size)
-		return 0;
+		goto error;
 
 	/*
 	 * If the hole extends beyond i_size, set the hole

@@ -4549,18 +4551,6 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
 	first_page_offset = first_page << PAGE_CACHE_SHIFT;
 	last_page_offset = last_page << PAGE_CACHE_SHIFT;
 
-	/*
-	 * Write out all dirty pages to avoid race conditions
-	 * Then release them.
-	 */
-	if (mapping->nrpages && mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
-		err = filemap_write_and_wait_range(mapping,
-			offset, offset + length - 1);
-
-		if (err)
-			return err;
-	}
-
 	/* Now release the pages */
 	if (last_page_offset > first_page_offset) {
 		truncate_pagecache_range(inode, first_page_offset,

@@ -4572,12 +4562,14 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
 
 	credits = ext4_writepage_trans_blocks(inode);
 	handle = ext4_journal_start(inode, credits);
-	if (IS_ERR(handle))
-		return PTR_ERR(handle);
+	if (IS_ERR(handle)) {
+		err = PTR_ERR(handle);
+		goto error;
+	}
 
 	err = ext4_orphan_add(handle, inode);
 	if (err)
-		goto out;
+		goto error;
 
 	/*
 	 * Now we need to zero out the non-page-aligned data in the

@@ -4652,6 +4644,8 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
 	ext4_ext_invalidate_cache(inode);
 	ext4_discard_preallocations(inode);
 
+	err = ext4_es_remove_space(inode, first_block,
+				   stop_block - first_block);
 	err = ext4_ext_remove_space(inode, first_block, stop_block - 1);
 
 	ext4_ext_invalidate_cache(inode);

@@ -4667,6 +4661,8 @@ out:
 	inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
 	ext4_mark_inode_dirty(handle, inode);
 	ext4_journal_stop(handle);
+error:
+	mutex_unlock(&inode->i_mutex);
 	return err;
 }
 int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,

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