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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 26 Dec 2020 09:57:13 -0800
Message-ID: <CAHk-=wiT50aEErZgZOrbFQ=GhFuM3MnBmHoSBSScN9rmXMnOKQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] mm: Allow architectures to request 'old' entries when prefaulting
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Hugh Dickins <hughd@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Will Deacon <will@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Jan Kara <jack@suse.cz>, Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vinayak Menon <vinmenon@codeaurora.org>,
        Android Kernel Team <kernel-team@android.com>
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On Fri, Dec 25, 2020 at 3:31 AM Kirill A. Shutemov <kirill@shutemov.name> wrote:
>
> The new helper next_page() returns a stablized page, so filemap_map_pmd()
> can clearly decide if we should set up a page table or a huge page.

I really like that next_page() abstraction, my only comment is that I
think it should be renamed as "next_stable_page()" or something, and
then this part:

+       if (!page)
+               page = xas_find(xas, end_pgoff);
+       else
+               page = xas_next_entry(xas, end_pgoff);

should be in the caller.

Then just have two helper functions like 'first_map_page()' and
'next_map_page()' which just do

        next_stable_page(xas_find(xas, end_pgoff))

and

        next_stable_page(xas_next_entry(xas, end_pgoff))

respectively.

Because not only does that get rid of the "if (page)" test, I think it
would make things a bit clearer. When I read the patch first, the
initial "next_page()" call confused me.

But maybe I'm just grasping at straws. Even in this format, I think
it's a nice cleanup and makes for more understandable code.

          Linus