Re: [PATCH 4/7] Use vfs __set_page_dirty interface instead of doing it inside filesystem

[Sage Weil <sage@inktank.com>]

On Wed, 4 Jul 2012, Sha Zhengju wrote:
> On 07/02/2012 10:49 PM, Sage Weil wrote:
> > On Mon, 2 Jul 2012, Sha Zhengju wrote:
> > > On 06/29/2012 01:21 PM, Sage Weil wrote:
> > > > On Thu, 28 Jun 2012, Sha Zhengju wrote:
> > > > 
> > > > > From: Sha Zhengju<handai.szj@taobao.com>
> > > > > 
> > > > > Following we will treat SetPageDirty and dirty page accounting as an
> > > > > integrated
> > > > > operation. Filesystems had better use vfs interface directly to avoid
> > > > > those details.
> > > > > 
> > > > > Signed-off-by: Sha Zhengju<handai.szj@taobao.com>
> > > > > ---
> > > > >    fs/buffer.c                 |    2 +-
> > > > >    fs/ceph/addr.c              |   20 ++------------------
> > > > >    include/linux/buffer_head.h |    2 ++
> > > > >    3 files changed, 5 insertions(+), 19 deletions(-)
> > > > > 
> > > > > diff --git a/fs/buffer.c b/fs/buffer.c
> > > > > index e8d96b8..55522dd 100644
> > > > > --- a/fs/buffer.c
> > > > > +++ b/fs/buffer.c
> > > > > @@ -610,7 +610,7 @@ EXPORT_SYMBOL(mark_buffer_dirty_inode);
> > > > >     * If warn is true, then emit a warning if the page is not uptodate
> > > > > and
> > > > > has
> > > > >     * not been truncated.
> > > > >     */
> > > > > -static int __set_page_dirty(struct page *page,
> > > > > +int __set_page_dirty(struct page *page,
> > > > >    		struct address_space *mapping, int warn)
> > > > >    {
> > > > >    	if (unlikely(!mapping))
> > > > This also needs an EXPORT_SYMBOL(__set_page_dirty) to allow ceph to
> > > > continue to build as a module.
> > > > 
> > > > With that fixed, the ceph bits are a welcome cleanup!
> > > > 
> > > > Acked-by: Sage Weil<sage@inktank.com>
> > > Further, I check the path again and may it be reworked as follows to avoid
> > > undo?
> > > 
> > > __set_page_dirty();
> > > __set_page_dirty();
> > > ceph operations;                ==>                     if (page->mapping)
> > > if (page->mapping)                                            ceph
> > > operations;
> > >      ;
> > > else
> > >      undo = 1;
> > > if (undo)
> > >      xxx;
> > Yep.  Taking another look at the original code, though, I'm worried that
> > one reason the __set_page_dirty() actions were spread out the way they are
> > is because we wanted to ensure that the ceph operations were always
> > performed when PagePrivate was set.
> > 
> 
> Sorry, I've lost something:
> 
> __set_page_dirty();                        __set_page_dirty();
> ceph operations;
> if(page->mapping)         ==>      if(page->mapping) {
>        SetPagePrivate;                            SetPagePrivate;
> else                                                      ceph operations;
>     undo = 1;                                  }
> 
> if (undo)
>     XXX;
> 
> I think this can ensure that ceph operations are performed together with
> SetPagePrivate.

Yeah, that looks right, as long as the ceph accounting operations happen 
before SetPagePrivate.  I think it's no more or less racy than before, at 
least. 

The patch doesn't apply without the previous ones in the series, it looks 
like.  Do you want to prepare a new version or should I?

Thanks!
sage

 
> > It looks like invalidatepage won't get called if private isn't set, and
> > presumably it handles the truncate race with __set_page_dirty() properly
> > (right?).  What about writeback?  Do we need to worry about writepage[s]
> > getting called with a NULL page->private?
> 
> __set_page_dirty does handle racing conditions with truncate and
> writeback writepage[s] also take page->private into consideration
> which is done inside specific filesystems. I notice that ceph has handled
> this in ceph_writepage().
> Sorry, not vfs expert and maybe I've not caught your point...
>
> 
> 
> Thanks,
> Sha
> 
> > Thanks!
> > sage
> > 
> > 
> > 
> > > 
> > > 
> > > Thanks,
> > > Sha
> > > 
> > > > > diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> > > > > index 8b67304..d028fbe 100644
> > > > > --- a/fs/ceph/addr.c
> > > > > +++ b/fs/ceph/addr.c
> > > > > @@ -5,6 +5,7 @@
> > > > >    #include<linux/mm.h>
> > > > >    #include<linux/pagemap.h>
> > > > >    #include<linux/writeback.h>	/* generic_writepages */
> > > > > +#include<linux/buffer_head.h>
> > > > >    #include<linux/slab.h>
> > > > >    #include<linux/pagevec.h>
> > > > >    #include<linux/task_io_accounting_ops.h>
> > > > > @@ -73,14 +74,8 @@ static int ceph_set_page_dirty(struct page *page)
> > > > >    	int undo = 0;
> > > > >    	struct ceph_snap_context *snapc;
> > > > > 
> > > > > -	if (unlikely(!mapping))
> > > > > -		return !TestSetPageDirty(page);
> > > > > -
> > > > > -	if (TestSetPageDirty(page)) {
> > > > > -		dout("%p set_page_dirty %p idx %lu -- already
> > > > > dirty\n",
> > > > > -		     mapping->host, page, page->index);
> > > > > +	if (!__set_page_dirty(page, mapping, 1))
> > > > >    		return 0;
> > > > > -	}
> > > > > 
> > > > >    	inode = mapping->host;
> > > > >    	ci = ceph_inode(inode);
> > > > > @@ -107,14 +102,7 @@ static int ceph_set_page_dirty(struct page *page)
> > > > >    	     snapc, snapc->seq, snapc->num_snaps);
> > > > >    	spin_unlock(&ci->i_ceph_lock);
> > > > > 
> > > > > -	/* now adjust page */
> > > > > -	spin_lock_irq(&mapping->tree_lock);
> > > > >    	if (page->mapping) {	/* Race with truncate? */
> > > > > -		WARN_ON_ONCE(!PageUptodate(page));
> > > > > -		account_page_dirtied(page, page->mapping);
> > > > > -		radix_tree_tag_set(&mapping->page_tree,
> > > > > -				page_index(page),
> > > > > PAGECACHE_TAG_DIRTY);
> > > > > -
> > > > >    		/*
> > > > >    		 * Reference snap context in page->private.  Also set
> > > > >    		 * PagePrivate so that we get invalidatepage callback.
> > > > > @@ -126,14 +114,10 @@ static int ceph_set_page_dirty(struct page
> > > > > *page)
> > > > >    		undo = 1;
> > > > >    	}
> > > > > 
> > > > > -	spin_unlock_irq(&mapping->tree_lock);
> > > > > -
> > > > >    	if (undo)
> > > > >    		/* whoops, we failed to dirty the page */
> > > > >    		ceph_put_wrbuffer_cap_refs(ci, 1, snapc);
> > > > > 
> > > > > -	__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
> > > > > -
> > > > >    	BUG_ON(!PageDirty(page));
> > > > >    	return 1;
> > > > >    }
> > > > > diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> > > > > index 458f497..0a331a8 100644
> > > > > --- a/include/linux/buffer_head.h
> > > > > +++ b/include/linux/buffer_head.h
> > > > > @@ -336,6 +336,8 @@ static inline void lock_buffer(struct buffer_head
> > > > > *bh)
> > > > >    }
> > > > > 
> > > > >    extern int __set_page_dirty_buffers(struct page *page);
> > > > > +extern int __set_page_dirty(struct page *page,
> > > > > +		struct address_space *mapping, int warn);
> > > > > 
> > > > >    #else /* CONFIG_BLOCK */
> > > > > 
> > > > > -- 
> > > > > 1.7.1
> > > > > 
> > > > > --
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> > > > > 
> > > 
> 
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