linux-kernel - Re: [RFC 02/19] cachefiles: implement key scheme for demand-read mode

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Message-ID: <269788.1639134293@warthog.procyon.org.uk>
Date:   Fri, 10 Dec 2021 11:04:53 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jeffle Xu <jefflexu@...ux.alibaba.com>
Cc:     dhowells@...hat.com, linux-cachefs@...hat.com, xiang@...nel.org,
        chao@...nel.org, linux-erofs@...ts.ozlabs.org,
        linux-fsdevel@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        bo.liu@...ux.alibaba.com, tao.peng@...ux.alibaba.com,
        gerry@...ux.alibaba.com, eguan@...ux.alibaba.com,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 02/19] cachefiles: implement key scheme for demand-read mode

Jeffle Xu <jefflexu@...ux.alibaba.com> wrote:

> Thus simplify the logic of placing backing files, in which backing files
> are under "cache/<volume>/" directory directly.

You then have a scalability issue on the directory inode lock - and there may
also be limits on the capacity of a directory.  The hash function is meant to
work the same, no matter the cpu arch, so you should be able to copy that to
userspace and derive the hash yourself.

> Also skip coherency checking currently to ease the development and debug.

Better if you can do that in erofs rather than cachefiles.  Just set your
coherency data to all zeros or something.

David