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Date:   Mon, 2 Mar 2020 22:34:00 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     Anshuman Khandual <anshuman.khandual@arm.com>
cc:     linux-mm@kvack.org, "David S. Miller" <davem@davemloft.net>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Hugh Dickins <hughd@google.com>, sparclinux@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [RFC 3/3] mm/vma: Introduce some more VMA flag wrappers
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On Mon, 2 Mar 2020, Anshuman Khandual wrote:

> This adds the following new VMA flag wrappers which will replace current
> open encodings across various places. This should not have any functional
> implications.
> 
> vma_is_dontdump()
> vma_is_noreserve()
> vma_is_special()
> vma_is_locked()
> vma_is_mergeable()
> vma_is_softdirty()
> vma_is_thp()
> vma_is_nothp()

Why?? Please don't. I am not at all keen on your 1/3 and 2/3 (some
of us actually like to see what the VM_ flags are where they're used,
without having to chase through scattered wrappers hiding them),
but this 3/3 particularly upset me.

There is a good reason for the (hideously named) is_vm_hugetlb_page(vma):
to save "#ifdef CONFIG_HUGETLB_PAGE"s all over (though I suspect the
same could have been achieved much more nicely by #define VM_HUGETLB 0);
but hiding all flags in vma_is_whatever()s is counter-productive churn.

Improved readability? Not to my eyes.

Hugh