linux-kernel - Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting

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Message-ID: <CAHk-=wgO2LsoKhX7MjSECo+Xrj1-Me7tzRfNcsdEZBRwJW1cQg@mail.gmail.com>
Date:   Fri, 18 Dec 2020 10:56:55 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Matthew Wilcox <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jan Kara <jack@...e.cz>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting

On Fri, Dec 18, 2020 at 3:04 AM Kirill A. Shutemov <kirill@...temov.name> wrote:
>
> This should do. See below.

Looks fine.

> > Then that second loop very naturally becomes a "do { } while ()" one.
>
> I don't see it. I haven't found a reasonable way to rework it do-while.

Now that you return early for the "HEAD == NULL" case, this loop:

        for (; head; head = xas_next_entry(&xas, end_pgoff)) {
                [...]
        }

very naturally becomes

        do {
                [...]
        } while ((head = xas_next_entry(&xas, end_pgoff)) != NULL);

because the initial test for 'head' being NULL is no longer needed,
and thus it's a lot more logical to just test it at the end of the
loop when we update it.

No?

Maybe I'm missing something silly.

           Linus