linux-kernel - Re: [PATCH v2] mm/uffd: UFFD_FEATURE_WP

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Date:   Thu, 2 Mar 2023 08:57:13 -0500
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Muhammad Usama Anjum <usama.anjum@...labora.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        "kernel@...labora.com" <kernel@...labora.com>
Subject: Re: [PATCH v2] mm/uffd: UFFD_FEATURE_WP_UNPOPULATED

On Thu, Mar 02, 2023 at 10:37:44AM +0100, David Hildenbrand wrote:
> Especially for such large sparse VMAs, the current way of allocating
> pagetables to place markers/zeropages is far from optimal.

IMHO that's not a generic workload.  As mentioned in the reply there, I
would suggest we go with simple then we have space to optimize it in the
future if necessary, because the API will be the same.

If I want to monitor a super sparse VMA on dirty, one thing I can already
try is register with MISSING + WP (!WP_UNPOPULATED).  It may be a good
intermediate solution to avoid any marker ovearheads.

-- 
Peter Xu