linux-kernel - Re: [PATCH 5/6] eventfs: get rid of dentry pointers without refcounts

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Message-ID: <CAHk-=wiPWaiD5fwyXXHX-qgk6t2+0NM_KHzwiecvCBiNWZacHA@mail.gmail.com>
Date: Tue, 30 Jan 2024 15:06:13 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] eventfs: get rid of dentry pointers without refcounts

On Tue, 30 Jan 2024 at 14:56, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> With that, the base size of 'struct eventfs_inode' actually becomes 96
> bytes for me.

It can be shrunk some more.

The field ordering is suboptimal. Pointers are 8 bytes and 8-byte
aligned, but 'struct kref' is just 4 bytes, and 'struct eventfs_attr'
is 12 bytes and 4-byte aligned.

So if you pack all the 8-byte-aligned fields at the beginning, and the
4-byte-aligned ones at the end, you get 88 bytes.

At which point a name pointer would *just* fit in 96 bytes.

..  and then some debug option is enabled, and it all goes to hell again.

              Linus