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SubjectRe: [PATCH 4/7] Use vfs __set_page_dirty interface instead of doing it inside filesystem
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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> > > > > linux-fsdevel"
> > > > > in
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> > > > >
> > > > >
> > >
>
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