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

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Date:   Tue, 16 Jul 2019 08:33:59 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Brendan Higgins <brendanhiggins@...gle.com>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
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        Luis Chamberlain <mcgrof@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
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        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

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.

> 
> 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?