llvm dev - Jul 2021 - RFC: Sanitizer-based Heap Profiler

On Thu, Jul 8, 2021 at 6:25 PM Teresa Johnson <tejohnson at google.com>
wrote:
> Responding to this one first, I'll respond to your other email shortly.
> Initially we plan to provide hints to tcmalloc via new APIs to help it make
> allocation decisions (things like hotness and lifetime). The compiler will
> be responsible for adding these hints, using some method to disambiguate
> the calling context (e.g. via function cloning, new parameter, etc).
>
Sounds good -- thanks!

(though this would increase code size and thus, instruction cache pressure
-- tsk, tsk... :-))
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On Thu, Jul 8, 2021 at 8:56 AM Andrey Bokhanko <andreybokhanko at
gmail.com>
wrote:
> On Thu, Jul 8, 2021 at 6:25 PM Teresa Johnson <tejohnson at
google.com>
> wrote:
>
>> Responding to this one first, I'll respond to your other email
shortly.
>> Initially we plan to provide hints to tcmalloc via new APIs to help it
make
>> allocation decisions (things like hotness and lifetime). The compiler
will
>> be responsible for adding these hints, using some method to
disambiguate
>> the calling context (e.g. via function cloning, new parameter, etc).
>>
> Sounds good -- thanks!
>
> (though this would increase code size and thus, instruction cache pressure
> -- tsk, tsk... :-))
>
There are various methods for disambiguating the contexts (e.g. HALO
inserts some instructions at a minimal number of callsites to do this), and
I suspect a hybrid method will be best in practice. E.g. cloning for hot
allocation contexts or callsites, and instructions or parameters or
something else on colder allocation contexts and callsites, to balance the
code size and dynamic instruction overheads.


-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |
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On Thu, Jul 8, 2021 at 8:56 AM Andrey Bokhanko <andreybokhanko at
gmail.com>
wrote:
> On Thu, Jul 8, 2021 at 6:25 PM Teresa Johnson <tejohnson at
google.com>
> wrote:
>
>> Responding to this one first, I'll respond to your other email
shortly.
>> Initially we plan to provide hints to tcmalloc via new APIs to help it
make
>> allocation decisions (things like hotness and lifetime). The compiler
will
>> be responsible for adding these hints, using some method to
disambiguate
>> the calling context (e.g. via function cloning, new parameter, etc).
>>
> Sounds good -- thanks!
>
> (though this would increase code size and thus, instruction cache pressure
> -- tsk, tsk... :-))
>
There are lots of ways to control the overhead : 1) context merging if
their properties are similar; 2) context merging if memory in each context
is short lived; 3) context trimming etc.
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