Re: Performance of ext4

[Holger Kiehl]

On Mon, 23 Jun 2008, Aneesh Kumar K.V wrote:

> On Fri, Jun 20, 2008 at 09:21:48AM +0000, Holger Kiehl wrote:
> > On Fri, 20 Jun 2008, Theodore Tso wrote:
> >
> > > On Fri, Jun 20, 2008 at 08:32:52AM +0000, Holger Kiehl wrote:
> > > > > It sounds like i_size is actually dropping in
> > > > > size at some pointer long after the file was written.  If I had to
> > >
> > > sorry, "at some point"...
> > >
> > > > > guess the value in the inode cache is correct; and perhaps so is the
> > > > > value on the journal.  But somehow, the wrong value is getting written
> > > > > to disk
> > >
> > > Or, "the right value is never getting written to disk".  (Which as I
> > > think about it is more likely; it's likely that an update to i_size is
> > > getting *lost*, perhaps because the delalloc code is possibly
> > > modifying i_size without starting a transaction first.  Again this is
> > > just a guess.)
> > >
> > > > What I find strange is that the missing parts of the file are not for
> > > > example exactly 512 or 1024 or 4096 bytes it is mostly some odd number
> > > > of bytes.
> > >
> > > Is there any chance the truncation point is related to how the program
> > > is writing its output file?  i.e., if it is a text file, is the
> > > truncation happening after a new-line or when the stdio library might
> > > have done an explicit or implicit fflush()?
> > When the benchmark runs it writes to stdout and with tee to the result
> > file. It first writes some information about the system, prepares the
> > test files (creates lots of small files), calls sync and then starts
> > the test. Then every minute one line gets written to the result file.
> > Often I have seen that everything after the sync was missing. But
> > sometimes it happened that some parts at the end are missing. But it
> > was always a clean cut, that is there where no lines that where cut
> > partially. The lines where always complete.
>
> I found one place where we fail to update i_disksize. Can you try this
> patch ?
Yes, I would like to however when I take
ext4-patch-queue-70acdb9605784bd5c4b06e1a19761828a494a337.tar.gz (which is
the current ext4-patch-queue from http://repo.or.cz/w/ext4-patch-queue.git)
and apply those to linux-2.6.26-rc6 I get the following reject:


***************
*** 574,579 ****
  	INIT_LIST_HEAD(&ei->i_prealloc_list);
  	spin_lock_init(&ei->i_prealloc_lock);
  	jbd2_journal_init_jbd_inode(&ei->jinode, &ei->vfs_inode);
  	return &ei->vfs_inode;
  }

--- 574,584 ----
  	INIT_LIST_HEAD(&ei->i_prealloc_list);
  	spin_lock_init(&ei->i_prealloc_lock);
  	jbd2_journal_init_jbd_inode(&ei->jinode, &ei->vfs_inode);
+ 	ei->i_reserved_data_blocks = 0;
+ 	ei->i_reserved_meta_blocks = 0;
+ 	ei->i_allocated_meta_blocks = 0;
+ 	ei->i_delalloc_reserved_flag = 0;
+ 	spin_lock_init(&(ei->i_block_reservation_lock));
  	return &ei->vfs_inode;
  }

Which is from delalloc-ext4-ENOSPC-handling.patch. What am I doing wrong?
I could apply this by hand but I do not know if this would be correct.
Please can anyone advice what I need to do?

Thanks,
Holger

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