linux-kernel - Re: [PATCH v9 03/18] kunit: test: add string_stream a std::stream like string builder

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Message-ID: <CAFd5g44bE0F=wq_fOAnxFTtoOyx1dUshhDAkKWr5hX9ipJ4Sxw@mail.gmail.com>
Date:   Mon, 15 Jul 2019 15:11:13 -0700
From:   Brendan Higgins <brendanhiggins@...gle.com>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
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        Rob Herring <robh@...nel.org>, shuah <shuah@...nel.org>,
        "Theodore Ts'o" <tytso@....edu>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
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Subject: Re: [PATCH v9 03/18] kunit: test: add string_stream a std::stream
 like string builder

On Mon, Jul 15, 2019 at 3:04 PM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Brendan Higgins (2019-07-15 14:11:50)
> > On Mon, Jul 15, 2019 at 1:43 PM Stephen Boyd <sboyd@...nel.org> wrote:
> > >
> > > I also wonder if it would be better to just have a big slop buffer of a
> > > 4K page or something so that we almost never have to allocate anything
> > > with a string_stream and we can just rely on a reader consuming data
> > > while writers are writing. That might work out better, but I don't quite
> > > understand the use case for the string stream.
> >
> > That makes sense, but might that also waste memory since we will
> > almost never need that much memory?
>
> Why do we care? These are unit tests.

Agreed.

> Having allocations in here makes
> things more complicated, whereas it would be simpler to have a pointer
> and a spinlock operating on a chunk of memory that gets flushed out
> periodically.

I am not so sure. I have to have the logic to allocate memory in some
case no matter what (what if I need more memory that my preallocated
chuck?). I think it is simpler to always request an allocation than to
only sometimes request an allocation.