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

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Message-ID: <CAFd5g47Nawp7V8=hetgBQWzWqmEyAz1GtWWwMrb9k=CCR33inQ@mail.gmail.com>
Date:   Tue, 16 Jul 2019 11:55:54 -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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        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 Tue, Jul 16, 2019 at 8:34 AM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Brendan Higgins (2019-07-15 15:43:20)
> > 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.
>
> Sure, sounds like a nice way to avoid duplicating similar logic to
> maintain a list of things to free later.

I think I will go that route for now.

> >
> > What do you think?
>
> If you go the allocation route then you'll need to have the flags to
> know what context you're in to allocate appropriately. Does that mean
> all the string operations will now take GFP flags?

We could set the GFP flags in the constructor, store them in a field,
and then just reuse them.

Thanks!