linux-kernel - Re: [PATCH v4 15/36] lib: introduce support for page allocation tagging

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Date: Tue, 27 Feb 2024 10:30:53 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>
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Subject: Re: [PATCH v4 15/36] lib: introduce support for page allocation
 tagging



On 2/26/24 18:11, Suren Baghdasaryan wrote:
> On Mon, Feb 26, 2024 at 9:07 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> On 2/21/24 20:40, Suren Baghdasaryan wrote:
>>> Introduce helper functions to easily instrument page allocators by
>>> storing a pointer to the allocation tag associated with the code that
>>> allocated the page in a page_ext field.
>>>
>>> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>>> Co-developed-by: Kent Overstreet <kent.overstreet@...ux.dev>
>>> Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
>>
>> The static key usage seems fine now. Even if the page_ext overhead is still
>> always paid when compiled in, you mention in the cover letter there's a plan
>> for boot-time toggle later, so
> 
> Yes, I already have a simple patch for that to be included in the next
> revision: https://github.com/torvalds/linux/commit/7ca367e80232345f471b77b3ea71cf82faf50954

This opt-out logic would require a distro kernel with allocation
profiling compiled-in to ship together with something that modifies
kernel command line to disable it by default, so it's not very
practical. Could the CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT be
turned into having 3 possible choices, where one of them would
initialize mem_profiling_enabled to false?

Or, taking a step back, is it going to be a common usecase to pay the
memory overhead unconditionally, but only enable the profiling later
during runtime? Also what happens if someone would enable and disable it
multiple times during one boot? Would the statistics get all skewed
because some frees would be not accounted while it's disabled?

>>
>> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
> 
> Thanks!
> 
>>
>>