Re: [PATCH v2 1/6] iomap: correct the range of a partial dirty clear

[Dave Chinner]

On Mon, Aug 12, 2024 at 09:33:39AM -0700, Darrick J. Wong wrote:
> On Mon, Aug 12, 2024 at 08:11:54PM +0800, Zhang Yi wrote:
> > From: Zhang Yi <yi.zhang@xxxxxxxxxx>
> > 
> > The block range calculation in ifs_clear_range_dirty() is incorrect when
> > partial clear a range in a folio. We can't clear the dirty bit of the
> > first block or the last block if the start or end offset is blocksize
> > unaligned, this has not yet caused any issue since we always clear a
> > whole folio in iomap_writepage_map()->iomap_clear_range_dirty(). Fix
> > this by round up the first block and round down the last block and
> > correct the calculation of nr_blks.
> > 
> > Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
> > ---
> >  fs/iomap/buffered-io.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> > index f420c53d86ac..4da453394aaf 100644
> > --- a/fs/iomap/buffered-io.c
> > +++ b/fs/iomap/buffered-io.c
> > @@ -138,11 +138,14 @@ static void ifs_clear_range_dirty(struct folio *folio,
> >  {
> >  	struct inode *inode = folio->mapping->host;
> >  	unsigned int blks_per_folio = i_blocks_per_folio(inode, folio);
> > -	unsigned int first_blk = (off >> inode->i_blkbits);
> > -	unsigned int last_blk = (off + len - 1) >> inode->i_blkbits;
> > -	unsigned int nr_blks = last_blk - first_blk + 1;
> > +	unsigned int first_blk = DIV_ROUND_UP(off, i_blocksize(inode));
> 
> Is there a round up macro that doesn't involve integer division?

i_blocksize() is supposed to be a power of 2, so yes:

/**
 * round_up - round up to next specified power of 2
 * @x: the value to round
 * @y: multiple to round up to (must be a power of 2)
 *
 * Rounds @x up to next multiple of @y (which must be a power of 2).
 * To perform arbitrary rounding up, use roundup() below.
 */
#define round_up(x, y) ((((x)-1) | __round_mask(x, y))+1)

-Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx