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From: Tejun Heo <tj@kernel.org>
To: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	Michal Koutny <mkoutny@suse.com>, Jens Axboe <axboe@kernel.dk>,
	Kees Cook <keescook@chromium.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jim Newsome <jnewsome@torproject.org>,
	Alexey Gladkov <legion@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Jann Horn <jannh@google.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Security Officers <security@kernel.org>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH 2/6] cgroup: Allocate cgroup_file_ctx for kernfs_open_file->priv
Date: Fri, 10 Dec 2021 08:38:02 -1000	[thread overview]
Message-ID: <YbOeiu5+DZQsJbm8@slm.duckdns.org> (raw)
In-Reply-To: <CAHk-=wgiYkECT=hZRKj8ZwfBPw2Uz=gpOGBGd4ny0KYhSsjC0w@mail.gmail.com>

Hello,

On Fri, Dec 10, 2021 at 09:53:41AM -0800, Linus Torvalds wrote:
> On Thu, Dec 9, 2021 at 1:47 PM Tejun Heo <tj@kernel.org> wrote:
> >
> > of->priv is currently used by each interface file implementation to store
> > private information. This patch collects the current two private data usages
> > into struct cgroup_file_ctx which is allocated and freed by the common path.
> > This allows generic private data which applies to multiple files, which will
> > be used to in the following patch.
> 
> I'm not sure if it's worth it having that union just to make the
> struct be 8 bytes instead of 16 (and later 16 bytes instead of 24),
> when the real cost is that dynamic allocation overhead, and there's
> likely only one or two active actual allocations at a time.

Yeah, I was initially doing ctx->procs_it and ->psi_trigger which looked
kinda silly so then nested structs and then why not the union which is kinda
logical in semantic sense.

> Wouldn't that simplify things? And might there not be some cgroup
> pressure user that also wants to use the iterator interfaces? Maybe
> not, my point is more that once we have an explicit struct allocation
> for cgroup proc files, we might as well clarify and simplify the
> code..

It's a bit of bikeshedding but I wanna explicitly denote who at currently
uses the fields, so how about nested structs w/ embedded iterator? If other
files ever want to share fields, we can shift those fields to the common
area together with ->ns.

Thanks.

-- 
tejun

  reply	other threads:[~2021-12-10 18:38 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-09 21:47 [PATCHSET cgroup/for-5.16-fixes] cgroup: Use open-time creds and namespace for migration perm checks Tejun Heo
2021-12-09 21:47 ` [PATCH 1/6] cgroup: Use open-time credentials for process migraton " Tejun Heo
2021-12-10 17:41   ` Linus Torvalds
2021-12-09 21:47 ` [PATCH 2/6] cgroup: Allocate cgroup_file_ctx for kernfs_open_file->priv Tejun Heo
2021-12-10 17:53   ` Linus Torvalds
2021-12-10 18:38     ` Tejun Heo [this message]
2021-12-10 18:45       ` Linus Torvalds
2021-12-10 19:06         ` Tejun Heo
2021-12-10 19:14           ` Linus Torvalds
2021-12-09 21:47 ` [PATCH 3/6] cgroup: Use open-time cgroup namespace for process migration perm checks Tejun Heo
2021-12-09 21:47 ` [PATCH 4/6] selftests: cgroup: Make cg_create() use 0755 for permission instead of 0644 Tejun Heo
2021-12-09 21:47 ` [PATCH 5/6] selftests: cgroup: Test open-time credential usage for migration checks Tejun Heo
2021-12-09 21:47 ` [PATCH 6/6] selftests: cgroup: Test open-time cgroup namespace " Tejun Heo
2021-12-13 19:18 [PATCHSET v2 cgroup/for-5.16-fixes] cgroup: Use open-time creds and namespace for migration perm checks Tejun Heo
2021-12-13 19:18 ` [PATCH 2/6] cgroup: Allocate cgroup_file_ctx for kernfs_open_file->priv Tejun Heo
2021-12-13 19:29   ` Linus Torvalds
2021-12-13 19:56     ` Tejun Heo
2021-12-14 17:03   ` Michal Koutný

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