linux-kernel - Re: [PATCH 0/3] mm,thp,rmap: rework the use of subpages

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Date:   Fri, 18 Nov 2022 12:51:09 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>, Peter Xu <peterx@...hat.com>,
        Yang Shi <shy828301@...il.com>,
        John Hubbard <jhubbard@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Mina Almasry <almasrymina@...gle.com>,
        James Houghton <jthoughton@...gle.com>,
        Zach O'Keefe <zokeefe@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/3] mm,thp,rmap: rework the use of subpages_mapcount

On Fri, 18 Nov 2022, Linus Torvalds wrote:
> On Fri, Nov 18, 2022 at 1:08 AM Hugh Dickins <hughd@...gle.com> wrote:
> >
> > Linus was underwhelmed by the earlier compound mapcounts series:
> > this series builds on top of it (as in next-20221117) to follow
> > up on his suggestions - except rmap.c still using lock_page_memcg(),
> > since I hesitate to steal the pleasure of deletion from Johannes.
> 
> This looks good to me. Particularly 2/3 made me go "Aww, yes" but the
> overall line removal stats look good too.
> 
> That said, I only looked at the patches, and not the end result
> itself. But not having the bit spin lock is, I think, a huge
> improvement.

Great, thanks a lot for looking through.

> 
> I do wonder if this should be now just merged with your previous
> series - it looks a bit odd how your previous series adds that
> bitlock, only for it to be immediately removed.
> 
> But if you think the logic ends up being easier to follow this way as
> two separate patch series, I guess I don't care.

I rather like having its evolution on record there, but that might just
be my sentimentality + laziness.  Kirill did a grand job of reviewing
the first series: I think that, at least for now, it would be easier
for people to review the changes if the two series are not recombined.

But the first series has not yet graduated from mm-unstable,
so if Andrew and/or Kirill also prefer to have them combined into one
bit_spin_lock-less series, that I can do.  (And the end result should be
identical, so would not complicate Johannes's lock_page_memcg() excision.)

Hugh

> 
> And the memcg locking is entirely a separate issue, and I hope
> Johannes will deal with that.
> 
> Thanks,
>               Linus