linux-kernel - Re: cleanup the walk_page

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Message-ID: <CAHk-=wiOB5wLWxHe8UDHnBB1DWrZaZ62ZPXnD0KiE8hYoWokNA@mail.gmail.com>
Date:   Fri, 16 Aug 2019 09:20:52 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Jason Gunthorpe <jgg@...lanox.com>,
        Christoph Hellwig <hch@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Hellström <thomas@...pmail.org>,
        Jerome Glisse <jglisse@...hat.com>,
        Steven Price <steven.price@....com>,
        Linux-MM <linux-mm@...ck.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Minchan Kim <minchan@...nel.org>
Subject: Re: cleanup the walk_page_range interface

On Fri, Aug 16, 2019 at 5:33 AM Christoph Hellwig <hch@....de> wrote:
>
> I see two new walk_page_range user in linux-next related to MADV_COLD
> support (which probably really should use walk_range_vma), and then
> there is the series from Steven, which hasn't been merged yet.

It does sound like this might as well just be handled in linux-next,
and there's no big advantage in me pulling the walker cleanups early.

Honestly, even if it ends up being handled as a conflict resolution
issue (rather than some shared branch), it probably simply isn't all
that painful. We have those kinds of semantic conflicts all the time,
it doesn't worry me too much.

So I'm not worried about new _users_ of the page walker concurrently
with the page walker interface itself being cleaned up. Those kinds of
conflicts end up being "just make sure to update the new users to the
new interface when they get pulled". Happens all the time.

I'd be more worried about two different branches wanting to change the
internal implementation of the page walker itself, and the actual
*code* itself getting conflicts (as opposed to the interface vs users
kind of conflicts). Those kinds of conflicts can be messy. But it
sounds like Thomas Hellström's changes aren't that kind of thing.

I'm still willing to do the early merge if it turns out to be hugely
helpful, but from the discussion so far it does sound like "just merge
during 5.4 merge window" is perfectly fine.

               Linus