From: Petr Pavlu <petr.pavlu@suse.com>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: gregkh@linuxfoundation.org, rafael@kernel.org, song@kernel.org,
lucas.de.marchi@gmail.com, lucas.demarchi@intel.com,
christophe.leroy@csgroup.eu, peterz@infradead.org,
rppt@kernel.org, dave@stgolabs.net, willy@infradead.org,
vbabka@suse.cz, mhocko@suse.com, dave.hansen@linux.intel.com,
colin.i.king@gmail.com, jim.cromie@gmail.com,
catalin.marinas@arm.com, jbaron@akamai.com,
rick.p.edgecombe@intel.com, yujie.liu@intel.com,
david@redhat.com, tglx@linutronix.de, hch@lst.de,
patches@lists.linux.dev, linux-modules@vger.kernel.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
pmladek@suse.com, prarit@redhat.com,
torvalds@linux-foundation.org, lennart@poettering.net
Subject: Re: [PATCH 2/2] module: add support to avoid duplicates early on load
Date: Thu, 25 May 2023 13:40:32 +0200 [thread overview]
Message-ID: <8fc5b26b-d2f6-0c8f-34a1-af085dbef155@suse.com> (raw)
In-Reply-To: <20230524213620.3509138-3-mcgrof@kernel.org>
On 5/24/23 23:36, Luis Chamberlain wrote:
> Add support to use the new kread_uniq_fd() to avoid duplicate kernel
> reads on modules. At the cost of about ~945 bytes to your kernel size,
> enabling this on a 255 CPU x86_64 qemu guest this saves about ~1.8 GiB
> of memory during boot which would otherwise be free'd, and reduces boot
> time by about ~11 seconds.
>
> Userspace loads modules through finit_module(), this in turn will
> use vmalloc space up to 3 times:
>
> a) The kernel_read_file() call
> b) Optional module decompression
> c) Our final copy of the module
>
> Commit 064f4536d139 ("module: avoid allocation if module is already
> present and ready") shows a graph of the amount of vmalloc space
> observed allocated but freed for duplicate module request which end
> up in the trash bin. Since there is a linear relationship with the
> number of CPUs eventually this will bite us and you end up not being
> able to boot. That commit put a stop gap for c) but to avoid the
> vmalloc() space wasted on a) and b) we need to detect duplicates
> earlier.
>
> We could just have userspace fix this, but as reviewed at LSFMM 2023
> this year in Vancouver, fixing this in userspace can be complex and we
> also can't know when userpace is fixed. Fixing this in kernel turned
> out to be easy with the inode and with a simple kconfig option we can
> let users / distros decide if this full stop gap is worthy to enable.
kmod normally uses finit_module() only if a module is not compressed,
otherwise it decompresses it first and then invokes init_module().
Looking at Fedora and openSUSE Tumbleweed, they compress kernel modules
with xz and zstd, respectively. They also have their kernels built
without any CONFIG_MODULE_COMPRESS_{GZIP,XZ,ZSTD} options.
It means that these and similarly organized distributions end up using
init_module(), and adding complexity to optimize finit_module() wouldn't
actually help in their case.
-- Petr
next prev parent reply other threads:[~2023-05-25 11:41 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 21:36 [PATCH 0/2] module: avoid all memory pressure due to duplicates Luis Chamberlain
2023-05-24 21:36 ` [PATCH 1/2] fs/kernel_read_file: add support for duplicate detection Luis Chamberlain
2023-05-24 21:52 ` Linus Torvalds
2023-05-24 21:56 ` Linus Torvalds
2023-05-24 22:07 ` Luis Chamberlain
2023-05-25 4:00 ` Linus Torvalds
2023-05-25 18:08 ` Luis Chamberlain
2023-05-25 18:35 ` Luis Chamberlain
2023-05-25 18:50 ` Linus Torvalds
2023-05-25 19:32 ` Luis Chamberlain
2023-05-25 7:01 ` Christian Brauner
2023-05-24 21:36 ` [PATCH 2/2] module: add support to avoid duplicates early on load Luis Chamberlain
2023-05-25 11:40 ` Petr Pavlu [this message]
2023-05-25 16:07 ` Linus Torvalds
2023-05-25 16:42 ` Greg KH
2023-05-25 18:22 ` Luis Chamberlain
2023-05-25 17:52 ` Linus Torvalds
2023-05-25 18:45 ` Lucas De Marchi
2023-05-25 21:12 ` Linus Torvalds
2023-05-25 22:02 ` Luis Chamberlain
2023-05-26 1:39 ` Linus Torvalds
2023-05-29 8:58 ` Johan Hovold
2023-05-29 11:00 ` Linus Torvalds
2023-05-29 12:44 ` Johan Hovold
2023-05-29 15:18 ` Johan Hovold
2023-05-30 1:55 ` Linus Torvalds
2023-05-30 9:40 ` Johan Hovold
2023-06-05 12:25 ` Johan Hovold
2023-05-30 16:22 ` Luis Chamberlain
2023-05-30 17:16 ` Lucas De Marchi
2023-05-30 19:41 ` Luis Chamberlain
2023-05-30 22:17 ` Linus Torvalds
2023-05-31 5:30 ` Lucas De Marchi
2023-05-31 0:31 ` Luis Chamberlain
2023-05-31 7:51 ` David Hildenbrand
2023-05-31 16:57 ` Luis Chamberlain
2023-06-02 15:19 ` David Hildenbrand
2023-06-02 16:04 ` Luis Chamberlain
2023-06-05 11:26 ` David Hildenbrand
2023-06-05 15:17 ` Luis Chamberlain
2023-06-05 15:28 ` Luis Chamberlain
2023-06-28 18:52 ` Luis Chamberlain
2023-06-28 20:14 ` Linus Torvalds
2023-06-28 22:07 ` Linus Torvalds
2023-06-28 23:17 ` Linus Torvalds
2023-06-29 0:18 ` Luis Chamberlain
2023-06-02 16:06 ` Linus Torvalds
2023-06-02 16:37 ` David Hildenbrand
2023-05-30 22:45 ` Dan Williams
2023-06-04 14:26 ` Rudi Heitbaum
2023-05-29 17:47 ` Linus Torvalds
2023-05-30 10:01 ` Johan Hovold
2023-05-25 16:54 ` Lucas De Marchi
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