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From: Luis Chamberlain <mcgrof@kernel.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Kees Cook <keescook@chromium.org>,
	Iurii Zaikin <yzaikin@google.com>,
	linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
	linux-mm@kvack.org, Ivan Teterevkov <ivan.teterevkov@nutanix.com>,
	Michal Hocko <mhocko@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	"Guilherme G . Piccoli" <gpiccoli@canonical.com>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Christian Brauner <christian.brauner@ubuntu.com>
Subject: Re: [PATCH v2 0/3] support setting sysctl parameters from kernel command line
Date: Thu, 16 Apr 2020 06:38:34 +0000	[thread overview]
Message-ID: <20200416063834.GO11244@42.do-not-panic.com> (raw)
In-Reply-To: <20200416150206.d3e103a1a5497b3518d4359c@kernel.org>

On Thu, Apr 16, 2020 at 03:02:06PM +0900, Masami Hiramatsu wrote:
> Hi Luis,
> 
> On Wed, 15 Apr 2020 06:30:41 +0000
> Luis Chamberlain <mcgrof@kernel.org> wrote:
> > Currently the maximum config size size is 32KB and the total key-words
> > (not     key-value entries) must be under 1024 nodes.  Note: this is not
> > the number of entries but nodes, an entry must consume more than 2 nodes
> > (a key-word and a value). So theoretically, it will be up to 512
> > key-value pairs. If keys contains 3 words in average, it can contain 256
> > key-value pairs. In most cases, the number of config items will be under
> > 100 entries and smaller than 8KB, so it would be enough.  If the node
> > number exceeds 1024, parser returns an error even if the file       size
> > is smaller than 32KB.  Anyway, since bootconfig command verifies it when
> > appending a boot config       to initrd image, user can notice it before
> > boot.  
> > ```
> > *recommending* bootconfig due to the limitation of cmdline seems
> > sensible, however if we advise that.. wouldn't the space for 512
> > theoretical entries full up rather fast?
> 
> Yeah, I think it is easier to hit the node number limitation rather
> than fill up the space. However, since the bootconfig supports comments,
> if user writes enough readable config file, I think it's probably the
> right balance :)
> If you think the 512 entries is too small, it is easy to expand it
> upto 32K (64K nodes). But it may consume 512KB memory only for the
> node (meta) data. Current 1024 nodes consumes 8KB (8bytes/node), so
> compared with the max data size (32KB), I think it is a better balance.

Yeah, and well at least x86 / x86_64 sets COMMAND_LINE_SIZE to 2048
right now (2 KB), that'd hit the limit of abuse of cmdline pretty fast
too. I see no way to scale this reasonably if people abuse syctls on
the command line but to use bootconfig and bite the bullet on size,
to keep sanity.

  Luis

  reply	other threads:[~2020-04-16  6:39 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-14 11:32 [PATCH v2 0/3] support setting sysctl parameters from kernel command line Vlastimil Babka
2020-04-14 11:32 ` [PATCH v2 1/3] kernel/sysctl: " Vlastimil Babka
2020-04-15  3:08   ` Kees Cook
2020-04-15  9:03   ` Masami Hiramatsu
2020-04-16  1:29     ` Luis Chamberlain
2020-04-16 10:49       ` Masami Hiramatsu
2020-04-16 15:53         ` Luis Chamberlain
2020-04-17 10:34           ` Masami Hiramatsu
2020-04-17 16:59             ` Luis Chamberlain
2020-04-18 10:12               ` Masami Hiramatsu
2020-04-14 11:32 ` [PATCH v2 2/3] kernel/sysctl: support handling command line aliases Vlastimil Babka
2020-04-14 11:32 ` [PATCH v2 3/3] kernel/hung_task convert hung_task_panic boot parameter to sysctl Vlastimil Babka
2020-04-15  3:23 ` [PATCH v2 0/3] support setting sysctl parameters from kernel command line Masami Hiramatsu
2020-04-15  6:30   ` Luis Chamberlain
2020-04-16  6:02     ` Masami Hiramatsu
2020-04-16  6:38       ` Luis Chamberlain [this message]
2020-04-15  8:56   ` Vlastimil Babka
2020-04-15 10:01     ` Michal Hocko
2020-04-16  6:08     ` Masami Hiramatsu

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