On Thu, Nov 01, 2012 at 04:22:54PM -0400, Jeff Layton wrote:
> On Thu, 1 Nov 2012 11:43:26 -0700
> Boaz Harrosh <bharrosh@xxxxxxxxxxx> wrote:
>
> > On 11/01/2012 12:58 AM, Darrick J. Wong wrote:
> > > Fix up the filesystems that provide their own ->page_mkwrite handlers to
> > > provide stable page writes if necessary.
> > >
> > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > > ---
> > > fs/9p/vfs_file.c | 1 +
> > > fs/afs/write.c | 4 ++--
> > > fs/ceph/addr.c | 1 +
> > > fs/cifs/file.c | 1 +
> > > fs/ocfs2/mmap.c | 1 +
> > > fs/ubifs/file.c | 4 ++--
> > > 6 files changed, 8 insertions(+), 4 deletions(-)
> > >
> > >
> > > diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
> > > index c2483e9..aa253f0 100644
> > > --- a/fs/9p/vfs_file.c
> > > +++ b/fs/9p/vfs_file.c
> > > @@ -620,6 +620,7 @@ v9fs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> > > lock_page(page);
> > > if (page->mapping != inode->i_mapping)
> > > goto out_unlock;
> > > + wait_on_stable_page_write(page);
> > >
> >
> > Good god thanks, yes please ;-)
> >
> > > return VM_FAULT_LOCKED;
> > > out_unlock:
> > > diff --git a/fs/afs/write.c b/fs/afs/write.c
> > > index 9aa52d9..39eb2a4 100644
> > > --- a/fs/afs/write.c
> > > +++ b/fs/afs/write.c
> > > @@ -758,7 +758,7 @@ int afs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> >
> > afs, is it not a network filesystem? which means that it has it's own emulated none-block-device
> > BDI, registered internally. So if you do need stable pages someone should call
> > bdi_require_stable_pages()
> >
> > But again since it is a network filesystem I don't see how it is needed, and/or it might be
> > taken care of already.
> >
> > > #ifdef CONFIG_AFS_FSCACHE
> > > fscache_wait_on_page_write(vnode->cache, page);
> > > #endif
> > > -
> > > + wait_on_stable_page_write(page);
> > > _leave(" = 0");
> > > - return 0;
> > > + return VM_FAULT_LOCKED;
> > > }
> > > diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
> >
> > CEPH for sure has it's own "emulated none-block-device BDI". This one is also
> > a pure networking filesystem.
> >
> > And it already does what it needs to do with wait_on_writeback().
> >
> > So i do not think you should touch CEPH
> >
> > > index 6690269..e9734bf 100644
> > > --- a/fs/ceph/addr.c
> > > +++ b/fs/ceph/addr.c
> > > @@ -1208,6 +1208,7 @@ static int ceph_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> > > set_page_dirty(page);
> > > up_read(&mdsc->snap_rwsem);
> > > ret = VM_FAULT_LOCKED;
> > > + wait_on_stable_page_write(page);
> > > } else {
> > > if (ret == -ENOMEM)
> > > ret = VM_FAULT_OOM;
> > > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> >
> > Cifs also self-BDI network filesystem, but
> >
> > > index edb25b4..a8770bf 100644
> > > --- a/fs/cifs/file.c
> > > +++ b/fs/cifs/file.c
> > > @@ -2997,6 +2997,7 @@ cifs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> > > struct page *page = vmf->page;
> > >
> > > lock_page(page);
> >
> > It waits by locking the page, that's cifs naive way of waiting for writeback
> >
> > > + wait_on_stable_page_write(page);
> >
> > Instead it could do better and not override page_mkwrite at all, and all it needs
> > to do is call bdi_require_stable_pages() at it's own registered BDI
> >
>
> Hmm...I don't know...
>
> I've never been crazy about using the page lock for this, but in the
> absence of a better way to guarantee stable pages, it was what I ended
> up with at the time. cifs_writepages will hold the page lock until
> kernel_sendmsg returns. At that point the TCP layer will have copied
> off the page data so it's safe to release it.
>
> With this change though, we're going to end up blocking until the
> writeback flag clears, right? And I think that will happen when the
> reply comes in? So, we'll end up blocking for much longer than is
> really necessary in page_mkwrite with this change.
That's a very good point to make-- network FSes can stop the stable-waiting
after the request is sent. Can I interest you in a new page flag (PG_stable)
that indicates when a page has to be held for stable write? Along with a
modification to wait_on_stable_page_write that uses the new PG_stable flag
instead of just writeback? Then, you can clear PG_stable right after the
sendmsg() and release the page for further activity without having to overload
the page lock.
I wrote a patch that does exactly that as part of my work to defer the
integrity checksumming until the last possible instant. However, I haven't
gotten that part to work yet, so I left the PG_stable patch out of this
submission. On the other hand, it sounds like you could use it.
--D
>
> --
> Jeff Layton <jlayton@xxxxxxxxx>
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