linux-kernel - Re: [PATCH 00/40] Memory allocation profiling

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Message-ID: <CAJuCfpFYq7CZS4y2ZiF+AJHRKwnyhmZCk_uuTwFse26DxGh-qQ@mail.gmail.com>
Date:   Wed, 3 May 2023 10:40:42 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Michal Hocko <mhocko@...e.com>, akpm@...ux-foundation.org,
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Subject: Re: [PATCH 00/40] Memory allocation profiling

On Wed, May 3, 2023 at 9:28 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Wed, 3 May 2023 08:09:28 -0700
> Suren Baghdasaryan <surenb@...gle.com> wrote:
>
> > There is another issue, which I think can be solved in a smart way but
> > will either affect performance or would require more memory. With the
> > tracing approach we don't know beforehand how many individual
> > allocation sites exist, so we have to allocate code tags (or similar
> > structures for counting) at runtime vs compile time. We can be smart
> > about it and allocate in batches or even preallocate more than we need
> > beforehand but, as I said, it will require some kind of compromise.
>
> This approach is actually quite common, especially since tagging every
> instance is usually overkill, as if you trace function calls in a running
> kernel, you will find that only a small percentage of the kernel ever
> executes. It's possible that you will be allocating a lot of tags that will
> never be used. If run time allocation is possible, that is usually the
> better approach.

True but the memory overhead should not be prohibitive here. As a
ballpark number, on my machine I see there are 4838 individual
allocation locations and each codetag structure is 32 bytes, so that's
152KB.

>
> -- Steve