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

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Message-ID: <20260119072932.GB2562@lst.de>
Date: Mon, 19 Jan 2026 08:29:32 +0100
From: Christoph Hellwig <hch@....de>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: Christoph Hellwig <hch@....de>, Hongbo Li <lihongbo22@...wei.com>,
	chao@...nel.org, brauner@...nel.org, djwong@...nel.org,
	amir73il@...il.com, 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

On Sat, Jan 17, 2026 at 12:21:16AM +0800, Gao Xiang wrote:
> Hi Christoph,
>
> On 2026/1/16 23:46, Christoph Hellwig wrote:
>> 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
>
> Page cache sharing should apply to different EROFS
> filesystem images on the same machine too, so the
> physical disk block number idea cannot be applied
> to this.

Oh.  That's kinda unexpected and adds another twist to the whole scheme.
So in that case the on-disk data actually is duplicated in each image
and then de-duplicated in memory only?  Ewwww...