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Date:   Sun, 13 Feb 2022 22:52:13 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     Vlastimil Babka <vbabka@suse.cz>
cc:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Alistair Popple <apopple@nvidia.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Rik van Riel <riel@surriel.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Yu Zhao <yuzhao@google.com>, Greg Thelen <gthelen@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 01/13] mm/munlock: delete page_mlock() and all its
 works
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On Thu, 10 Feb 2022, Vlastimil Babka wrote:
> On 2/9/22 23:28, Hugh Dickins wrote:
> > 
> > Though taking this apart and putting it back together brings its own
> > dangers.  That second suggestion probably won't fly very well, with
> > 06/13 using mlock_count only while on the unevictable.  I'm not sure
> > how much rethinking the bisection possibility deserves.
> 
> Right, if it's impractical to change for a potential and hopefully unlikely
> bad bisection luck, just a note at the end of each patch's changelog
> mentioning what temporarily doesn't work, should be enough.

I'm adding a paragraph on that to the end of this 01/13's changelog.
If you or akpm think it's better  duplicated in 02, 03, 04, 05, 06
then I think it will be easiest if Andrew edits it into them, rather
than me updating them one by one.

> > As to VM_LOCKED: yes, you're right, at this stage of the series the
> > munlock really ought to be clearing VM_LOCKED (even while it doesn't
> > go on to do anything about the pages), as it claims in the comment above.
> > I removed this line at a later stage (07/13), when changing it to
> > mlock_vma_pages_range() serving both mlock and munlock according to
> > whether VM_LOCKED is provided - and mistakenly folded back that deletion
> > to this patch.  End result the same, but better to restore that maskout
> > in this patch, as you suggest.
> 
> Great, thanks. That restores any effect on VM_LOCKONFAULT in any case as well.

Yes, it turned out to be a mistake in my rebasing the series, the original
had the VM_LOCKED_CLEAR_MASK masking still there (up until the interface
changes in 07/13).  Thanks for spotting that.

Vlastimil, many thanks for your valiant effort reviewing this series:
it's not at all easy, and I much appreciate the time you've put into it.

I'm now going to send out v2 updates to 01, 04, 07, 10, 11 (only),
still based on 5.17-rc2, but incorporating your and others' suggestions.

Hugh