linux-kernel - Re: [PATCH v3] iomap: support tail packing inline read

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Date:   Mon, 19 Jul 2021 17:31:51 +0200
From:   Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:     Matthew Wilcox <willy@...radead.org>, linux-erofs@...ts.ozlabs.org,
        Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Andreas Gruenbacher <andreas.gruenbacher@...il.com>
Subject: Re: [PATCH v3] iomap: support tail packing inline read

Am Mo., 19. Juli 2021 um 17:29 Uhr schrieb Gao Xiang
<hsiangkao@...ux.alibaba.com>:
> On Mon, Jul 19, 2021 at 04:02:30PM +0100, Matthew Wilcox wrote:
> > On Mon, Jul 19, 2021 at 10:47:47PM +0800, Gao Xiang wrote:
> > > @@ -246,18 +245,19 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> > >     unsigned poff, plen;
> > >     sector_t sector;
> > >
> > > -   if (iomap->type == IOMAP_INLINE) {
> > > -           WARN_ON_ONCE(pos);
> > > -           iomap_read_inline_data(inode, page, iomap);
> > > -           return PAGE_SIZE;
> > > -   }
> > > -
> > > -   /* zero post-eof blocks as the page may be mapped */
> > >     iop = iomap_page_create(inode, page);
> > > +   /* needs to skip some leading uptodated blocks */
> > >     iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
> > >     if (plen == 0)
> > >             goto done;
> > >
> > > +   if (iomap->type == IOMAP_INLINE) {
> > > +           iomap_read_inline_data(inode, page, iomap, pos);
> > > +           plen = PAGE_SIZE - poff;
> > > +           goto done;
> > > +   }
> >
> > This is going to break Andreas' case that he just patched to work.
> > GFS2 needs for there to _not_ be an iop for inline data.  That's
> > why I said we need to sort out when to create an iop before moving
> > the IOMAP_INLINE case below the creation of the iop.
>
> I have no idea how it breaks Andreas' case from the previous commit
> message: "
> iomap: Don't create iomap_page objects for inline files
> In iomap_readpage_actor, don't create iop objects for inline inodes.
> Otherwise, iomap_read_inline_data will set PageUptodate without setting
> iop->uptodate, and iomap_page_release will eventually complain.
>
> To prevent this kind of bug from occurring in the future, make sure the
> page doesn't have private data attached in iomap_read_inline_data.
> "
>
> After this patch, iomap_read_inline_data() will set iop->uptodate with
> iomap_set_range_uptodate() rather than set PageUptodate() directly,
> so iomap_page_release won't complain.

Yes, that actually looks fine.

Thanks,
Andreas