Message-ID: <fd206791-aa8a-5cd8-2606-58d395f2c995@redhat.com>
Date:   Wed, 8 Mar 2023 18:04:22 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.8.0
Subject: Re: [PATCH v3 1/2] mm/uffd: UFFD_FEATURE_WP_UNPOPULATED
Content-Language: en-US
To:     Peter Xu <peterx@redhat.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Muhammad Usama Anjum <usama.anjum@collabora.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Axel Rasmussen <axelrasmussen@google.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Paul Gofman <pgofman@codeweavers.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20230306213925.617814-1-peterx@redhat.com>
 <20230306213925.617814-2-peterx@redhat.com>
 <94be7b9f-c33e-c6dc-4132-6cb78f7c0624@redhat.com> <ZAiqPU0RX3JfDFRP@x1n>
 <83b3f3ad-19a2-3737-77dd-3c3f9db82194@redhat.com> <ZAi8+PCsIzExWPQN@x1n>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <ZAi8+PCsIzExWPQN@x1n>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 08.03.23 17:51, Peter Xu wrote:
> On Wed, Mar 08, 2023 at 04:57:55PM +0100, David Hildenbrand wrote:
>> Oh, my thinking was that with markers you postpone placing the shared
>> zeropage. So the next read access will require a pagefault to map the shared
>> zeropage. Your v1 would have performed best in that case I guess.
> 
> Ah, so I misunderstood because the sentence being quote was in another
> context I think..

Sorry, I might have messed up the quoting.

> 
> Pagemap may bring overhead constantly though, not sure when vs page faults.
> May relevant to num of missing pages.

Right, one idea (raised by Dave G. IIRC) was to to the pagemap scanning 
concurrently from another thread and avoid most of the shared-zeropage 
dance.

-- 
Thanks,

David / dhildenb