linux-kernel - Re: [PATCH v15 5/9] erofs: introduce the page cache share feature

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Message-ID: <20260116154623.GC21174@lst.de>
Date: Fri, 16 Jan 2026 16:46:23 +0100
From: Christoph Hellwig <hch@....de>
To: Hongbo Li <lihongbo22@...wei.com>
Cc: hsiangkao@...ux.alibaba.com, chao@...nel.org, brauner@...nel.org,
	djwong@...nel.org, amir73il@...il.com, hch@....de,
	linux-fsdevel@...r.kernel.org, linux-erofs@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v15 5/9] erofs: introduce the page cache share feature

I don't really understand the fingerprint idea.  Files with the
same content will point to the same physical disk blocks, so that
should be a much better indicator than a finger print?  Also how does
the fingerprint guarantee uniqueness?  Is it a cryptographically
secure hash?  In here it just seems like an opaque blob.

> +static inline int erofs_inode_set_aops(struct inode *inode,
> +				       struct inode *realinode, bool no_fscache)

Factoring this out first would be a nice little prep patch.
Also it would probably be much cleaner using IS_ENABLED.

> +static int erofs_ishare_file_open(struct inode *inode, struct file *file)
> +{
> +	struct inode *sharedinode = EROFS_I(inode)->sharedinode;

Ok, it looks like this allocates a separate backing file and inode.