linux-kernel - [PATCH] modules: Use a better scheme for refcounting

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Date:	Thu, 15 May 2008 22:40:37 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Mike Travis <travis@....com>
Subject: [PATCH] modules: Use a better scheme for refcounting

Current refcounting for modules (done if CONFIG_MODULE_UNLOAD=y)
is using a lot of memory.

Each 'struct module' contains an [NR_CPUS] array of full cache lines.

This patch uses existing infrastructure (percpu_modalloc() & 
percpu_modfree())
to allocate percpu space for the refcount storage.

Instead of wasting NR_CPUS*128 bytes (on i386), we now use
num_possible_cpus*sizeof(local_t) bytes.

On a typical distro, where NR_CPUS=8, shiping 2000 modules, we reduce
size of module files by about 2 Mbytes. (1Kb per module)

Instead of having all refcounters in the same memory node - with TLB misses
because of vmalloc() - this new implementation permits to have better
NUMA properties, since each  CPU will use storage on its preferred node,
thanks to percpu storage.

Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
---
 include/linux/module.h |   25 ++++++++++++++++---------
 kernel/module.c        |   37 +++++++++++++++++++++++++++----------
 2 files changed, 43 insertions(+), 19 deletions(-)

View attachment "module.patch" of type "text/plain" (4857 bytes)