linux-kernel - Re: [PATCH v2] squashfs: cache partial compressed blocks

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Date:   Mon, 15 May 2023 12:31:49 +0000
From:   Vincent Whitchurch <Vincent.Whitchurch@...s.com>
To:     "hch@....de" <hch@....de>
CC:     kernel <kernel@...s.com>,
        "squashfs-devel@...ts.sourceforge.net" 
        <squashfs-devel@...ts.sourceforge.net>,
        "pliard@...gle.com" <pliard@...gle.com>,
        "phillip@...ashfs.org.uk" <phillip@...ashfs.org.uk>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] squashfs: cache partial compressed blocks

On Mon, 2023-05-15 at 12:03 +0200, Christoph Hellwig wrote:
> On Fri, May 12, 2023 at 03:18:05PM +0200, Vincent Whitchurch wrote:
> >  static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
> >  			     struct bio **biop, int *block_offset)
> >  {
> >  	struct squashfs_sb_info *msblk = sb->s_fs_info;
> > +	struct inode *cache_inode = msblk->cache_inode;
> > +	struct address_space *cache_mapping = cache_inode ? cache_inode->i_mapping : NULL;
> 
> Unless I'm badly misreading the squashfs_fill_super changes,
> cache_inode can't ever be NULL here or anywhere else in the I/O
> code.

Hmm, in this patch, cache_inode is only created if devblksize is
PAGE_SIZE, so it could be NULL if CONFIG_SQUASHFS_4K_DEVBLK_SIZE is not
set (or if PAGE_SIZE is greater than 4 KiB), right?

I'll fix the rest of your comments in an upcoming v3.  Thank you for the
review.