linux-kernel - Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle

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Message-ID: <CAPcyv4j642Hs4N2rHFEuEON1kQMwf-D0hzROPVFhcaWAK6rpdw@mail.gmail.com>
Date:   Tue, 23 Jun 2020 14:15:24 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH v2 2/3] mm/memory_hotplug: document why shuffle_zone() is relevant

On Mon, Jun 22, 2020 at 12:28 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 20.06.20 03:41, Dan Williams wrote:
> > On Fri, Jun 19, 2020 at 6:00 AM David Hildenbrand <david@...hat.com> wrote:
> >>
> >> It's not completely obvious why we have to shuffle the complete zone, as
> >> some sort of shuffling is already performed when onlining pages via
> >> __free_one_page(), placing MAX_ORDER-1 pages either to the head or the tail
> >> of the freelist. Let's document why we have to shuffle the complete zone
> >> when exposing larger, contiguous physical memory areas to the buddy.
> >>
> >
> > How about?
> >
> > Fixes: e900a918b098 ("mm: shuffle initial free memory to improve
> > memory-side-cache utilization")
> >
> > ...just like Patch1 since that original commit was missing the proper
> > commentary in the code?
>
> Hmm, mixed feelings. I (working for a distributor :) ) prefer fixes tags
> for actual BUGs, as described in
>
> Documentation/process/submitting-patches.rst: "If your patch fixes a bug
> in a specific commit, e.g. you found an issue using ``git bisect``,
> please use the 'Fixes:' tag with the first 12 characters" ...
>
> So unless there are strong feelings, I'll not add a fixes tag (although
> I agree, that it should have been contained in the original commit).

It doesn't need to be "Fixes", but how about at least mentioning the
original commit as a breadcrumb so that some future "git blame"
archaeology effort is streamlined.