Re: "orphaned pagecache memleak fix" question.

[Chris Mason <mason@suse.com>]

On Wednesday 06 April 2005 17:30, Andrew Morton wrote:
> Chris Mason <mason@suse.com> wrote:
> > On Wednesday 06 April 2005 03:58, Andrew Morton wrote:
> > > >  - wouldn't it be simpler to unconditionally remove page from LRU in
> > > >  ->invalidatepage()?
> > >
> > > I guess that's an option, yes.  If the fs cannot successfully
> > > invalidate the page then it can either block (as described above) or
> > > remove the page from the LRU.  The fs then wholly owns the page.
> > >
> > > I think it would be better to make ->invalidatepage always succeed
> > > though. The situation is probably rare.
> >
> > In data=journal it isn't rare at all.  Dropping the page from the lru
> > would be the best solution I think.
>
> Does that mean that my printk comes out?

To trigger the printk, you've got to stand on your head (at least for reiser3)

1) data=journal needs to log a file data buffer
2) The transaction starts to commit
3) Before the committing transaction calls mark_buffer_dirty on the data 
buffer, the file is truncated
4) The transaction commit calls mark_buffer_dirty, but only if the blocks 
corresponding to this buffer have not been freed on disk.  

It's the filesystem truncate call that frees the blocks, so the commit 
operation has to pop up in between the truncate_inodes_pages and 
inode->i_op->truncate().  The only way I found to make this happen reliably 
is to sprinkle schedules and busy loops into critical sections.

-chris
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