linux-kernel - Re: [PATCH 00/13] mm/munlock: rework of mlock+munlock page handling

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Date:   Wed, 9 Feb 2022 08:21:17 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     Michal Hocko <mhocko@...e.com>
cc:     Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Alistair Popple <apopple@...dia.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Rik van Riel <riel@...riel.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Yu Zhao <yuzhao@...gle.com>, Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 00/13] mm/munlock: rework of mlock+munlock page
 handling

On Wed, 9 Feb 2022, Michal Hocko wrote:
> 
> So far I have only managed to read through the series and trying to put
> all the pieces together (so far I have given up on the THP part) and my
> undestanding is far from complete. But I have to say I like the general
> approach and overall simplification.

Many thanks for looking, Michal, and for all the positivity!

> 
> The only thing that is not entirely clear to me at the moment is why you
> have chosen to ignore already mapped LOCKONFAULT pages. They will
> eventually get sorted out during the reclaim/migration but this can
> backfire if too many pages have been pre-faulted before LOCKONFAULT
> call. Maybe not an interesting case in the first place but I am still
> wondering why you have chosen that way.

I'm puzzled: what makes you think I'm ignoring already mapped LOCKONFAULT
pages?  I'd consider that a bug.

It is the case, isn't it, that a VM_LOCKONFAULT area always has VM_LOCKED
set too?  If I've got that wrong, yes, I'll need to revisit conditions.

> 
> I will be off next couple of days and plan to revisit this afterwards
> (should time allow). Anyway thanks a lot Hugh!
> -- 
> Michal Hocko
> SUSE Labs