On Mon, 23 Jul 2012, Zheng Liu wrote: > Date: Mon, 23 Jul 2012 19:57:22 +0800 > From: Zheng Liu <gnehzuil.liu@xxxxxxxxx> > To: Lukáš Czerner <lczerner@xxxxxxxxxx> > Cc: linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, > xiaoqiangnk@xxxxxxxxx, achender@xxxxxxxxxxxxxxxxxx, wenqing.lz@xxxxxxxxxx > Subject: Re: [RFC][PATCH 09/10 v1][RESEND] ext4: don't need to writeout all > dirty pages in punch hole > > Hi Lukas, > > On Mon, Jul 23, 2012 at 01:01:53PM +0200, Lukáš Czerner wrote: > > On Sun, 22 Jul 2012, Zheng Liu wrote: > > > > > Date: Sun, 22 Jul 2012 15:59:45 +0800 > > > From: Zheng Liu <gnehzuil.liu@xxxxxxxxx> > > > To: linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx > > > Cc: xiaoqiangnk@xxxxxxxxx, achender@xxxxxxxxxxxxxxxxxx, wenqing.lz@xxxxxxxxxx > > > Subject: [RFC][PATCH 09/10 v1][RESEND] ext4: don't need to writeout all dirty > > > pages in punch hole > > > > > > From: Zheng Liu <wenqing.lz@xxxxxxxxxx> > > > > > > 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. :-) Great, thanks! > > > 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? You're absolutely right, currently this is possible. But I think that we can take i_data_sem before truncating the pagecache hence preventing anyone from mapping new blocks. However this is not yet implemented in my patch set. ... hmm, looking at the ext4_write_begin() it seems like it might not be such good idea after all. It seems to take page lock before i_data_sem so we might get deadlock, moreover if the punch hole happened in the middle of the ext4_write_begin() we might have only part of the data written, moreover this does not have to be hole aligned, which is bad. I need to revise that. Thanks! -Lukas > > Regards, > Zheng > > > > > > > Signed-off-by: Zheng Liu <wenqing.lz@xxxxxxxxxx> > > > --- > > > 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, > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html >
