linux-kernel - Re: [PATCH 4/4] iomap: don't abandon the whole copy when we have iomap_folio

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Message-ID: <tcaz35lk5kwkmj74sv4fbf52fliha4uc2yv5fjee2qxsjamqr2@jkxk3vitf7lp>
Date: Mon, 15 Sep 2025 13:29:10 +0200
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Jinliang Zheng <alexjlzheng@...il.com>
Cc: alexjlzheng@...cent.com, brauner@...nel.org, djwong@...nel.org, 
	hch@...radead.org, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-xfs@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH 4/4] iomap: don't abandon the whole copy when we have
 iomap_folio_state

On Mon, Sep 15, 2025 at 07:12:28PM +0800, Jinliang Zheng wrote:
> On Mon, 15 Sep 2025 12:50:54 +0200, kernel@...kajraghav.com wrote:
> > > +static int iomap_trim_tail_partial(struct inode *inode, loff_t pos,
> > > +		size_t copied, struct folio *folio)
> > > +{
> > > +	struct iomap_folio_state *ifs = folio->private;
> > > +	unsigned block_size, last_blk, last_blk_bytes;
> > > +
> > > +	if (!ifs || !copied)
> > > +		return 0;
> > > +
> > > +	block_size = 1 << inode->i_blkbits;
> > > +	last_blk = offset_in_folio(folio, pos + copied - 1) >> inode->i_blkbits;
> > > +	last_blk_bytes = (pos + copied) & (block_size - 1);
> > > +
> > > +	if (!ifs_block_is_uptodate(ifs, last_blk))
> > > +		copied -= min(copied, last_blk_bytes);
> > 
> > If pos is aligned to block_size, is there a scenario where 
> > copied < last_blk_bytes?
> 
> I believe there is no other scenario. The min() here is specifically to handle cases where
> pos is not aligned to block_size. But please note that the pos here is unrelated to the pos
> in iomap_adjust_read_range().

Ah, you are right. This is about write and not read. I got a bit
confused after reading both the patches back to back.

--
Pankaj