linux-kernel - Re: [PATCH] cramfs: generate unique inode number for better inode cache usage

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Message-ID: <AANLkTinPkGHASWubtUY1aDbnxv8V3uGvV+b+e+TkSiVS@mail.gmail.com>
Date:	Tue, 14 Dec 2010 13:08:54 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	stefani@...bold.net, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] cramfs: generate unique inode number for better inode
 cache usage

On Tue, Dec 14, 2010 at 12:51 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
>
> Did you look at using iunique() to generate cramfs inode numbers?

That breaks the cramfs "hardlinking" (which is just files that have
the same data pointer), and now a hardlinked file wouldn't have the
same inode number any more.

Of course, I'm not sure the hardlinking really matters. cramfs
hardlinks aren't really traditional hardlinks anyway - since the
permissions etc are in the directory entry, you can have the data
hardlinked without having the same permissions, so it's not a "real"
hardlink even if the inode number were to be the same.

But this patch seems to roughly approximate the old pseudo-hardlink
behavior. It used to be that all non-data files showed up with the
same inode number, now they have separate inode numbers.

That said, I hate how it moves that "setup_inode" helper function
inline and then does the "if it's a character device" kinds of tests
twice. Once for the inode number logic, and once for the inode
operations structure assignment.

So I think the approach is fine, but I think the implementation is pretty ugly.

                          Linus
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