Re: [PATCH] mm: drop "wait" parameter from write_one_page

[Jeff Layton]

On Wed, 2017-03-08 at 00:34 -0800, John Hubbard wrote:
> On 03/05/2017 05:23 AM, Jeff Layton wrote:
> > The callers all have it set to 1 anyway. Also, make it clear that this
> > function will not set any sort of AS_* error, and that the caller must
> > do so if necessary.
> 
> Hi Jeff,
> 
> Silly nit: The above bit about not setting AS_* errors seems to not have made it 
> into the write_one_page() comment header. I see that it now says it will 
> (unconditionally) wait on IO, which implies no async IO errors, that's true. But 
> also the part about the caller setting having to set that...makes it look like you 
> intended to document this in the code, but got interrupted, maybe?
> 
> The code changes look perfect, though. And although I'm not a fs guy, it seems 
> pretty clear that with all the callers passing in 1 all this time, nobody is likely 
> to complain about this simplification.
> 
> thanks,
> John Hubbard
> NVIDIA
> 

Thanks for having a look. That blurb in the changelog refers to the
kerneldoc comment over write_one_page below...

> 
>   No existing caller uses this on normal files, so
> > none of them need it.
> > 
> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > ---
> >  fs/exofs/dir.c        |  2 +-
> >  fs/ext2/dir.c         |  2 +-
> >  fs/jfs/jfs_metapage.c |  4 ++--
> >  fs/minix/dir.c        |  2 +-
> >  fs/sysv/dir.c         |  2 +-
> >  fs/ufs/dir.c          |  2 +-
> >  include/linux/mm.h    |  2 +-
> >  mm/page-writeback.c   | 14 +++++++-------
> >  8 files changed, 15 insertions(+), 15 deletions(-)
> > 
> > diff --git a/fs/exofs/dir.c b/fs/exofs/dir.c
> > index 42f9a0a0c4ca..e163ed980c20 100644
> > --- a/fs/exofs/dir.c
> > +++ b/fs/exofs/dir.c
> > @@ -72,7 +72,7 @@ static int exofs_commit_chunk(struct page *page, loff_t pos, unsigned len)
> >  	set_page_dirty(page);
> > 
> >  	if (IS_DIRSYNC(dir))
> > -		err = write_one_page(page, 1);
> > +		err = write_one_page(page);
> >  	else
> >  		unlock_page(page);
> > 
> > diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
> > index d9650c9508e4..e2709695b177 100644
> > --- a/fs/ext2/dir.c
> > +++ b/fs/ext2/dir.c
> > @@ -100,7 +100,7 @@ static int ext2_commit_chunk(struct page *page, loff_t pos, unsigned len)
> >  	}
> > 
> >  	if (IS_DIRSYNC(dir)) {
> > -		err = write_one_page(page, 1);
> > +		err = write_one_page(page);
> >  		if (!err)
> >  			err = sync_inode_metadata(dir, 1);
> >  	} else {
> > diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
> > index 489aaa1403e5..744fa3c079e6 100644
> > --- a/fs/jfs/jfs_metapage.c
> > +++ b/fs/jfs/jfs_metapage.c
> > @@ -711,7 +711,7 @@ void force_metapage(struct metapage *mp)
> >  	get_page(page);
> >  	lock_page(page);
> >  	set_page_dirty(page);
> > -	write_one_page(page, 1);
> > +	write_one_page(page);
> >  	clear_bit(META_forcewrite, &mp->flag);
> >  	put_page(page);
> >  }
> > @@ -756,7 +756,7 @@ void release_metapage(struct metapage * mp)
> >  		set_page_dirty(page);
> >  		if (test_bit(META_sync, &mp->flag)) {
> >  			clear_bit(META_sync, &mp->flag);
> > -			write_one_page(page, 1);
> > +			write_one_page(page);
> >  			lock_page(page); /* write_one_page unlocks the page */
> >  		}
> >  	} else if (mp->lsn)	/* discard_metapage doesn't remove it */
> > diff --git a/fs/minix/dir.c b/fs/minix/dir.c
> > index 7edc9b395700..baa9721f1299 100644
> > --- a/fs/minix/dir.c
> > +++ b/fs/minix/dir.c
> > @@ -57,7 +57,7 @@ static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
> >  		mark_inode_dirty(dir);
> >  	}
> >  	if (IS_DIRSYNC(dir))
> > -		err = write_one_page(page, 1);
> > +		err = write_one_page(page);
> >  	else
> >  		unlock_page(page);
> >  	return err;
> > diff --git a/fs/sysv/dir.c b/fs/sysv/dir.c
> > index 5bdae85ceef7..f5191cb2c947 100644
> > --- a/fs/sysv/dir.c
> > +++ b/fs/sysv/dir.c
> > @@ -45,7 +45,7 @@ static int dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
> >  		mark_inode_dirty(dir);
> >  	}
> >  	if (IS_DIRSYNC(dir))
> > -		err = write_one_page(page, 1);
> > +		err = write_one_page(page);
> >  	else
> >  		unlock_page(page);
> >  	return err;
> > diff --git a/fs/ufs/dir.c b/fs/ufs/dir.c
> > index de01b8f2aa78..48609f1d9580 100644
> > --- a/fs/ufs/dir.c
> > +++ b/fs/ufs/dir.c
> > @@ -53,7 +53,7 @@ static int ufs_commit_chunk(struct page *page, loff_t pos, unsigned len)
> >  		mark_inode_dirty(dir);
> >  	}
> >  	if (IS_DIRSYNC(dir))
> > -		err = write_one_page(page, 1);
> > +		err = write_one_page(page);
> >  	else
> >  		unlock_page(page);
> >  	return err;
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index b84615b0f64c..e17ebedba623 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2094,7 +2094,7 @@ extern void filemap_map_pages(struct vm_fault *vmf,
> >  extern int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
> > 
> >  /* mm/page-writeback.c */
> > -int write_one_page(struct page *page, int wait);
> > +int write_one_page(struct page *page);
> >  void task_dirty_inc(struct task_struct *tsk);
> > 
> >  /* readahead.c */
> > diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> > index 290e8b7d3181..855278fc538e 100644
> > --- a/mm/page-writeback.c
> > +++ b/mm/page-writeback.c
> > @@ -2360,15 +2360,16 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
> >  }
> > 
> >  /**
> > - * write_one_page - write out a single page and optionally wait on I/O
> > + * write_one_page - write out a single page and wait on I/O
> >   * @page: the page to write
> > - * @wait: if true, wait on writeout
> >   *
> >   * The page must be locked by the caller and will be unlocked upon return.
> >   *
> > - * write_one_page() returns a negative error code if I/O failed.
> > + * write_one_page() returns a negative error code if I/O failed. Note that
> > + * the address_space is not marked for error. The caller must do this if
> > + * needed.

...specifically the single sentence in the comment above.

As I said, none of the existing callers need to set an error in the
mapping when this fails, so I just added this to make it clear for any
new callers in the future.

> >   */
> > -int write_one_page(struct page *page, int wait)
> > +int write_one_page(struct page *page)
> >  {
> >  	struct address_space *mapping = page->mapping;
> >  	int ret = 0;
> > @@ -2379,13 +2380,12 @@ int write_one_page(struct page *page, int wait)
> > 
> >  	BUG_ON(!PageLocked(page));
> > 
> > -	if (wait)
> > -		wait_on_page_writeback(page);
> > +	wait_on_page_writeback(page);
> > 
> >  	if (clear_page_dirty_for_io(page)) {
> >  		get_page(page);
> >  		ret = mapping->a_ops->writepage(page, &wbc);
> > -		if (ret == 0 && wait) {
> > +		if (ret == 0) {
> >  			wait_on_page_writeback(page);
> >  			if (PageError(page))
> >  				ret = -EIO;
> > 

-- 
Jeff Layton <jlayton@xxxxxxxxxx>