linux-kernel - Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for inode

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Message-id: <20141017171229.7c1a113e@rohitk-ubuntu.sisodomain.com>
Date:	Fri, 17 Oct 2014 17:12:29 +0530
From:	Rohit <rohit.kr@...sung.com>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	akpm@...ux-foundation.org, james.l.morris@...cle.com,
	serge@...lyn.com, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, cpgs@...sung.com,
	pintu.k@...sung.com, vishnu.ps@...sung.com, iqbal.ams@...sung.com,
	ed.savinay@...sung.com, me.rohit@...e.com, pintu_agarwal@...oo.com
Subject: Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for
 inode_smack

On Thu, 16 Oct 2014 09:24:01 -0700
Casey Schaufler <casey@...aufler-ca.com> wrote:

> On 10/15/2014 5:10 AM, Rohit wrote:
> > The patch use kmem_cache to allocate/free inode_smack since they are
> > alloced in high volumes making it a perfect case for kmem_cache.
> >
> > As per analysis, 24 bytes of memory is wasted per allocation due
> > to internal fragmentation. With kmem_cache, this can be avoided.
> 
> What impact does this have on performance? I am much more
> concerned with speed than with small amount of memory.
> 
I think there should not be any performance problem as such.
However, please let me know how to check the performance in this case.

As far as i know, kzalloc first finds the kmalloc_index corresponding to
the size to get the kmem_cache_object and then calls kmem_cache_alloc
with the kmalloc_index(kmem_cache object). Here, we create kmem_cache
object specific for inode_smack and directly calls kmem_cache_alloc()
which should give better performance as compared to kzalloc.

Please let me know your comments.
> >
> > Accounting of memory allocation is below :
> >  total       slack            net      count-alloc/free
> > caller Before (with kzalloc)
> > 1919872      719952          1919872      29998/0
> > new_inode_smack+0x14
> >
> > After (with kmem_cache)
> > 1201680          0           1201680      30042/0
> > new_inode_smack+0x18
> >
> > >From above data, we found that 719952 bytes(~700 KB) of memory is
> > saved on allocation of 29998 smack inodes.
> >
> > Signed-off-by: Rohit <rohit.kr@...sung.com>
> > ---
> > Added static in kmem_cache object declaration noted by Andrew
> > Morton <akpm@ linux-foundation.org> . Also updated commit message.
> >  security/smack/smack_lsm.c |   13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> > index d515ec2..15d985c 100644
> > --- a/security/smack/smack_lsm.c
> > +++ b/security/smack/smack_lsm.c
> > @@ -53,6 +53,7 @@
> >  #define SMK_SENDING	2
> >  
> >  LIST_HEAD(smk_ipv6_port_list);
> > +static struct kmem_cache *smack_inode_cache;
> >  
> >  #ifdef CONFIG_SECURITY_SMACK_BRINGUP
> >  static void smk_bu_mode(int mode, char *s)
> > @@ -240,7 +241,7 @@ struct inode_smack *new_inode_smack(struct
> > smack_known *skp) {
> >  	struct inode_smack *isp;
> >  
> > -	isp = kzalloc(sizeof(struct inode_smack), GFP_NOFS);
> > +	isp = kmem_cache_zalloc(smack_inode_cache, GFP_NOFS);
> >  	if (isp == NULL)
> >  		return NULL;
> >  
> > @@ -767,7 +768,7 @@ static int smack_inode_alloc_security(struct
> > inode *inode) */
> >  static void smack_inode_free_security(struct inode *inode)
> >  {
> > -	kfree(inode->i_security);
> > +	kmem_cache_free(smack_inode_cache, inode->i_security);
> >  	inode->i_security = NULL;
> >  }
> >  
> > @@ -4264,10 +4265,16 @@ static __init int smack_init(void)
> >  	if (!security_module_enable(&smack_ops))
> >  		return 0;
> >  
> > +	smack_inode_cache = KMEM_CACHE(inode_smack, 0);
> > +	if (!smack_inode_cache)
> > +		return -ENOMEM;
> > +
> >  	tsp = new_task_smack(&smack_known_floor,
> > &smack_known_floor, GFP_KERNEL);
> > -	if (tsp == NULL)
> > +	if (tsp == NULL) {
> > +		kmem_cache_destroy(smack_inode_cache);
> >  		return -ENOMEM;
> > +	}
> >  
> >  	printk(KERN_INFO "Smack:  Initializing.\n");
> >  
> 

Thanks,
Rohit
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