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Date:   Mon, 1 May 2023 10:47:01 -0700
From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Suren Baghdasaryan <surenb@google.com>
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Subject: Re: [PATCH 00/40] Memory allocation profiling
Message-ID: <ZE/7FZbd31qIzrOc@P9FQF9L96D>
References: <20230501165450.15352-1-surenb@google.com>
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On Mon, May 01, 2023 at 09:54:10AM -0700, Suren Baghdasaryan 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 is performance
> comparison between the baseline kernel, profiling when enabled, profiling
> when disabled (nomem_profiling=y) and (for comparison purposes) baseline
> with CONFIG_MEMCG_KMEM enabled and allocations using __GFP_ACCOUNT:
> 
> 			kmalloc			pgalloc
> Baseline (6.3-rc7)	9.200s			31.050s
> profiling disabled	9.800 (+6.52%)		32.600 (+4.99%)
> profiling enabled	12.500 (+35.87%)	39.010 (+25.60%)
> memcg_kmem enabled	41.400 (+350.00%)	70.600 (+127.38%)

Hm, this makes me think we have a regression with memcg_kmem in one of
the recent releases. When I measured it a couple of years ago, the overhead
was definitely within 100%.

Do you understand what makes the your profiling drastically faster than kmem?

Thanks!