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Subject: Re: [PATCH v3] lib: stackdepot: Add support to configure
 STACK_HASH_SIZE
To:     Alexander Potapenko <glider@google.com>
Cc:     Minchan Kim <minchan@kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        dan.j.williams@intel.com, broonie@kernel.org,
        Masami Hiramatsu <mhiramat@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@google.com>, qcai@redhat.com,
        ylal@codeaurora.org, vinmenon@codeaurora.org
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From:   Vijayanand Jitta <vjitta@codeaurora.org>
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Date:   Thu, 17 Dec 2020 11:08:10 +0530
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On 12/16/2020 7:04 PM, Alexander Potapenko wrote:
>>> To reiterate, I think you don't need a tunable stack_hash_order
>>> parameter if the only use case is to disable the stack depot.
>>> Maybe it is enough to just add a boolean flag?
>>
>> There are multiple users of stackdepot they might still want to use
>> stack depot but with a lower memory footprint instead of MAX_SIZE
>> so, a configurable size might help here ?
> 
> Can you provide an example of a use case in which the user wants to
> use the stack depot of a smaller size without disabling it completely,
> and that size cannot be configured statically?
> As far as I understand, for the page owner example you gave it's
> sufficient to provide a switch that can disable the stack depot if
> page_owner=off.
> 
There are two use cases here,

1. We don't want to consume memory when page_owner=off ,boolean flag
would work here.

2. We would want to enable page_owner on low ram devices but we don't
want stack depot to consume 8 MB of memory, so for this case we would
need a configurable stack_hash_size so that we can still use page_owner
with lower memory consumption.

So, a configurable stack_hash_size would work for both these use cases,
we can set it to '0' for first case and set the required size for the
second case.

>>> Or even go further and disable the stack depot in the same place that
>>> disables page owner, as the user probably doesn't want to set two
>>> flags instead of one?
>>>
>>
>> Since, page owner is not the only user of stack depot we can't take that
>> decision of disabling stack depot if page owner is disabled.
> 
> Agreed, but if multiple subsystems want to use stackdepot together, it
> is even harder to estimate the total memory consumption.
> How likely is it that none of them will need MAX_SIZE?
> 
>>>> Minchan,
>>>> This should be fine right ? Do you see any issue with disabling
>>>> stack depot completely ?
>>>>
>>>> Thanks,
>>>> Vijay
>>>>
>>>>>> Thanks,
>>>>>> Vijay
>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Vijay
>>>>>>>>>
>>>>>>>>>>> Thanks,
>>>>>>>>>>> Vijay
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>>>>>>> member of Code Aurora Forum, hosted by The Linux Foundation
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>>>>> member of Code Aurora Forum, hosted by The Linux Foundation
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>> --
>>>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>>>> member of Code Aurora Forum, hosted by The Linux Foundation
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>>>> member of Code Aurora Forum, hosted by The Linux Foundation
>>>
>>>
>>>
>>
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
>> member of Code Aurora Forum, hosted by The Linux Foundation
> 
> 
> 

-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of Code Aurora Forum, hosted by The Linux Foundation