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

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Message-ID: <CAFd5g47y4vDB2P=EsGN8305LGeQPCTveNs-Jd5-=6K-XKY==CA@mail.gmail.com>
Date:   Mon, 15 Jul 2019 15:43:20 -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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        Peter Zijlstra <peterz@...radead.org>,
        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 3:11 PM Brendan Higgins
<brendanhiggins@...gle.com> wrote:
>
> 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.

Another even simpler alternative might be to just allocate memory
using kunit_kmalloc as we need it and just let the kunit_resource code
handle cleaning it all up when the test case finishes.

What do you think?