linux-kernel - Re: [PATCH v3 00/35] Memory allocation profiling

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Date: Wed, 14 Feb 2024 14:59:05 -0800
From: Tim Chen <tim.c.chen@...ux.intel.com>
To: Suren Baghdasaryan <surenb@...gle.com>, Yosry Ahmed
 <yosryahmed@...gle.com>
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Subject: Re: [PATCH v3 00/35] Memory allocation profiling

On Wed, 2024-02-14 at 12:30 -0800, Suren Baghdasaryan wrote:
> On Wed, Feb 14, 2024 at 12:17 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> > 
> > > > > Performance overhead:
> > > > > To evaluate performance we implemented an in-kernel test executing
> > > > > multiple get_free_page/free_page and kmalloc/kfree calls with allocation
> > > > > sizes growing from 8 to 240 bytes with CPU frequency set to max and CPU
> > > > > affinity set to a specific CPU to minimize the noise. Below are results
> > > > > from running the test on Ubuntu 22.04.2 LTS with 6.8.0-rc1 kernel on
> > > > > 56 core Intel Xeon:
> > > > > 
> > > > >                         kmalloc                 pgalloc
> > > > > (1 baseline)            6.764s                  16.902s
> > > > > (2 default disabled)    6.793s (+0.43%)         17.007s (+0.62%)
> > > > > (3 default enabled)     7.197s (+6.40%)         23.666s (+40.02%)
> > > > > (4 runtime enabled)     7.405s (+9.48%)         23.901s (+41.41%)
> > > > > (5 memcg)               13.388s (+97.94%)       48.460s (+186.71%)
> > > 
> > > (6 default disabled+memcg)    13.332s (+97.10%)         48.105s (+18461%)
> > > (7 default enabled+memcg)     13.446s (+98.78%)       54.963s (+225.18%)
> > 
> > I think these numbers are very interesting for folks that already use
> > memcg. Specifically, the difference between 6 & 7, which seems to be
> > ~0.85% and ~14.25%. IIUC, this means that the extra overhead is
> > relatively much lower if someone is already using memcgs.
> 
> Well, yes, percentage-wise it's much lower. If you look at the
> absolute difference between 6 & 7 vs 2 & 3, it's quite close.
> 
> > 
> > > 
> > > (6) shows a bit better performance than (5) but it's probably noise. I
> > > would expect them to be roughly the same. Hope this helps.
> > > 
> > > > 

Thanks for the data.  It does show that turning on memcg does not cost
extra overhead percentage wise.

Tim