Re: [RFC][PATCH 09/10 v1][RESEND] ext4: don't need to writeout all dirty pages in punch hole

Lukáš Czerner
2012-07-23T11:02:05Z

On Sun, 22 Jul 2012, Zheng Liu wrote:

> Date: Sun, 22 Jul 2012 15:59:45 +0800
> From: Zheng Liu <gnehzuil.liu@gmail.com>
> 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 <wenqing.lz@taobao.com>
>
> 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

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.

Thanks!
-Lukas

>
> Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
> ---
> 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,
>