Messages in this thread | | | Date | Sun, 26 Oct 2014 17:41:37 -0700 | From | Casey Schaufler <> | Subject | Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for inode_smack |
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On 10/17/2014 10:37 AM, Casey Schaufler wrote: > On 10/17/2014 9:34 AM, PINTU KUMAR wrote: >> Hi, >> >> >>> ________________________________ >>> From: Casey Schaufler <casey@schaufler-ca.com> >>> To: Rohit <rohit.kr@samsung.com> >>> Cc: akpm@linux-foundation.org; james.l.morris@oracle.com; serge@hallyn.com; linux-security-module@vger.kernel.org; linux-kernel@vger.kernel.org; cpgs@samsung.com; pintu.k@samsung.com; vishnu.ps@samsung.com; iqbal.ams@samsung.com; ed.savinay@samsung.com; me.rohit@live.com; pintu_agarwal@yahoo.com; Casey Schaufler <casey@schaufler-ca.com> >>> Sent: Friday, 17 October 2014 8:08 PM >>> Subject: Re: [PATCH v2] Security: smack: replace kzalloc with kmem_cache for inode_smack >>> >>> >>> On 10/17/2014 4:42 AM, Rohit wrote: >>>> On Thu, 16 Oct 2014 09:24:01 -0700 >>>> Casey Schaufler <casey@schaufler-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. >>> Any inode intensive benchmark would suffice. Even the classic >>> kernel build would do. >>> >>>> 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. >>> That would be my guess as well, but performance is tricky. Sometimes >>> things that "obviously" make performance better make it worse. There can >>> be unanticipated side effects. >>> >>> >>>> Please let me know your comments. >>> If you can run any sort of test that demonstrates this change >>> does not have performance impact, I'm fine with it. Smack is being >>> used in small devices, and both memory use and performance are critical >>> to the success of these devices. Of the two, performance is currently >>> more of an issue. >>> >> SMACK is used heavily in Tizen. We verified these changes for one of Tizen project. >> During boot time we observed that this object is used heavily, as identified by kmalloc-accounting. >> After replacing this we did not observe any difference in boot time. Also there was no side-effects seen so far. >> If you know of any other tests, please let us know. >> We will also try to gather some performance stats and present here. > We need to be somewhat more precise than "did not observe any > difference in boot time". The ideal benchmark would perform lots > of changes to the filesystem without doing lots of IO. One process > that matches that profile fairly well is a kernel make. I would be > satisfied with something as crude as using time(1) on a small (5?) > number of clean kernel makes each with and without the patch on the > running kernel. At the level of accuracy you usually get from time(1) > you won't find trivial differences, but if the change is a big problem > (or a big win) we'll know.
I have not seen anything indicating that the requested performance measurements have been done. I have no intention of accepting this without assurance that performance has not been damaged. I request that no one else carry this forward, either. The performance impact of security facilities comes under too much scrutiny to ignore it.
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