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 <20201111230601.GA984367@elver.google.com>
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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Thu, 12 Nov 2020 21:11:43 +0100
Message-ID: <CAAeHK+wwC7zETg_0VQab-mMhssNwC0_aoh3HqRVqN9SrZTMSKA@mail.gmail.com>
Subject: Re: [PATCH v2 18/20] kasan: clean up metadata allocation and usage
To:     Marco Elver <elver@google.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Nov 12, 2020 at 12:06 AM Marco Elver <elver@google.com> wrote:
>
> > +     /* Limit it with KMALLOC_MAX_SIZE (relevant for SLAB only). */
> > +     if (optimal_size > KMALLOC_MAX_SIZE)
> > +             optimal_size = KMALLOC_MAX_SIZE;
> > +     /* Use optimal size if the size with added metas is not large enough. */
>
> Uses the optimal size if it's not "too large" rather than "not large
> enough", right?

Not really. If the redzone composed from metas is begger than optimal
redzone - we're good. If it's not large enough to reach optimal
redzone - we need to make it bigger.

> As it is worded now makes me think this is a fallback,
> whereas ideally it's the common case, right?

It's hard to say which case is more common, as optimal redzone size
varies and depends on the object size.

[...]

Will fix the rest of the comments, thanks!