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Date: Tue, 16 Feb 2016 17:53:38 -0700
From: David Ahern <dsa@...ulusnetworks.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Edward Cree <ec429@...tab.net>
Cc: linux-kernel@...r.kernel.org
Subject: Re: Idea for reducing sysfs memory usage
On 2/16/16 5:47 PM, Greg Kroah-Hartman wrote:
> How many sysfs entries are you creating for that 20kb? And how did you
> measure it? If you don't access the files, the backing store is not
> allocated, saving you a lot of memory. If you do access it, it will be
> freed later on afterward, so it's sometimes really hard to measure this
> accurately.
Using the kmem tracepoints:
perf record -g \
-e
kmem:kmalloc,kmem:kmem_cache_alloc,kmem:mm_page_alloc,kmem:kfree,kmem:kmem_cache_free,kmem:mm_page_free
-- ip link add dummy1 type dummy
First go round I painstakenly examined each allocation and location.
After that I modified perf-kmem to do the summary for me for other use
cases.
I can forward the full notes if you want them. Here's the first few and
last few:
################
# sysfs -- start
# directory
# device_add -> kobject_add -- register with generic layer
ip 1732 [005] 27128.556548: kmem:kmalloc: ptr=0xffff8800ba9a5d60
bytes_req=7 bytes_alloc=32 gfp_flags=37748928
ffffffff8113e5ce __kmalloc_track_caller ([kernel.kallsyms])
ffffffff81116643 kstrdup ([kernel.kallsyms])
ffffffff8111667c kstrdup_const ([kernel.kallsyms])
ffffffff811a6bf5 __kernfs_new_node ([kernel.kallsyms])
ffffffff811a7397 kernfs_new_node ([kernel.kallsyms])
ffffffff811a7813 kernfs_create_dir_ns ([kernel.kallsyms])
ffffffff811a95f0 sysfs_create_dir_ns ([kernel.kallsyms])
ffffffff8126f76f kobject_add_internal ([kernel.kallsyms])
ffffffff8126fa62 kobject_add ([kernel.kallsyms])
ffffffff81319317 device_add ([kernel.kallsyms])
ffffffff81408528 netdev_register_kobject ([kernel.kallsyms])
ffffffff813f2cbb register_netdevice ([kernel.kallsyms])
ffffffff81401314 rtnl_newlink ([kernel.kallsyms])
# directory
ip 1732 [005] 27128.556555: kmem:kmem_cache_alloc:
ptr=0xffff8801399d6018 bytes_req=168 bytes_alloc=168 gfp_flags=37781696
ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms])
ffffffff811a6c0e __kernfs_new_node ([kernel.kallsyms])
ffffffff811a7397 kernfs_new_node ([kernel.kallsyms])
ffffffff811a7813 kernfs_create_dir_ns ([kernel.kallsyms])
ffffffff811a95f0 sysfs_create_dir_ns ([kernel.kallsyms])
ffffffff8126f76f kobject_add_internal ([kernel.kallsyms])
ffffffff8126fa62 kobject_add ([kernel.kallsyms])
ffffffff81319317 device_add ([kernel.kallsyms])
ffffffff81408528 netdev_register_kobject ([kernel.kallsyms])
ffffffff813f2cbb register_netdevice ([kernel.kallsyms])
ffffffff81401314 rtnl_newlink ([kernel.kallsyms])
# device_add -> device_create_file(dev, &dev_attr_uevent) -->
sysfs_create_file(&dev->kobj, &attr->attr)
ip 1732 [005] 27128.556583: kmem:kmem_cache_alloc:
ptr=0xffff8801399d60c0 bytes_req=168 bytes_alloc=168 gfp_flags=37781696
ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms])
ffffffff811a6c0e __kernfs_new_node ([kernel.kallsyms])
ffffffff811a7397 kernfs_new_node ([kernel.kallsyms])
ffffffff811a8ac7 __kernfs_create_file ([kernel.kallsyms])
ffffffff811a9310 sysfs_add_file_mode_ns ([kernel.kallsyms])
ffffffff811a9370 sysfs_create_file_ns ([kernel.kallsyms])
ffffffff81317f3b device_create_file ([kernel.kallsyms])
ffffffff81319342 device_add ([kernel.kallsyms])
ffffffff81408528 netdev_register_kobject ([kernel.kallsyms])
ffffffff813f2cbb register_netdevice ([kernel.kallsyms])
ffffffff81401314 rtnl_newlink ([kernel.kallsyms])
...
ip 1732 [005] 27128.560734: kmem:kmem_cache_alloc:
ptr=0xffff8800b94758a0 bytes_req=168 bytes_alloc=168 gfp_flags=37781696
ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms])
ffffffff811a6c0e __kernfs_new_node ([kernel.kallsyms])
ffffffff811a7397 kernfs_new_node ([kernel.kallsyms])
ffffffff811a8ac7 __kernfs_create_file ([kernel.kallsyms])
ffffffff811a9310 sysfs_add_file_mode_ns ([kernel.kallsyms])
ffffffff811a9cd2 internal_create_group ([kernel.kallsyms])
ffffffff811a9e20 sysfs_create_group ([kernel.kallsyms])
ffffffff814083ca netdev_queue_update_kobjects ([kernel.kallsyms])
ffffffff81408583 netdev_register_kobject ([kernel.kallsyms])
ffffffff813f2cbb register_netdevice ([kernel.kallsyms])
ffffffff81401314 rtnl_newlink ([kernel.kallsyms])
ip 1732 [005] 27128.560789: kmem:kmem_cache_alloc:
ptr=0xffff880139cd0400 bytes_req=256 bytes_alloc=256 gfp_flags=37748928
ffffffff8113ee09 kmem_cache_alloc ([kernel.kallsyms])
ffffffff813df48a __alloc_skb ([kernel.kallsyms])
ffffffff81270485 kobject_uevent_env ([kernel.kallsyms])
ffffffff81270703 kobject_uevent ([kernel.kallsyms])
ffffffff814083da netdev_queue_update_kobjects ([kernel.kallsyms])
ffffffff81408583 netdev_register_kobject ([kernel.kallsyms])
ffffffff813f2cbb register_netdevice ([kernel.kallsyms])
ffffffff81401314 rtnl_newlink ([kernel.kallsyms])
ip 1732 [005] 27128.560798: kmem:kmalloc: ptr=0xffff8800bab97c00
bytes_req=512 bytes_alloc=512 gfp_flags=37814976
ffffffff8113e5ce __kmalloc_track_caller ([kernel.kallsyms])
ffffffff813def36 __kmalloc_reserve.isra.50 ([kernel.kallsyms])
ffffffff813df4bc __alloc_skb ([kernel.kallsyms])
ffffffff81270485 kobject_uevent_env ([kernel.kallsyms])
ffffffff81270703 kobject_uevent ([kernel.kallsyms])
ffffffff814083da netdev_queue_update_kobjects ([kernel.kallsyms])
ffffffff81408583 netdev_register_kobject ([kernel.kallsyms])
ffffffff813f2cbb register_netdevice ([kernel.kallsyms])
ffffffff81401314 rtnl_newlink ([kernel.kallsyms])
# end netdev_register_kobject
###############################
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