linux-kernel - Re: [PATCH 1/2] fs/proc/task_mmu: add guard region bit to pagemap

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Message-ID: <dfdc09c1-fc66-4c78-9ff7-93fb2a1b6ee1@redhat.com>
Date: Mon, 24 Feb 2025 14:28:59 +0100
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
 Suren Baghdasaryan <surenb@...gle.com>, Kalesh Singh
 <kaleshsingh@...gle.com>, "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
 "Paul E . McKenney" <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>,
 Juan Yescas <jyescas@...gle.com>, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 linux-api@...r.kernel.org
Subject: Re: [PATCH 1/2] fs/proc/task_mmu: add guard region bit to pagemap

>> My thinking was, that if you have a large VMA, with ordinary pagemap you
>> have to copy 8byte per entry (and have room for that somewhere in user
>> space). In theory, with the scanning feature, you can leave that ...
>> scanning to the kernel and don't have to do any copying/allocate space for
>> it in user space etc.
> 
> That makes perfect sense!
> 
> I think this one will go a little lower on priorities + I'll come back to it but
> I"ll put it on the one reliable todo list I have, the whiteboard in my home
> office :) everything on that list at least eventually gets looked at, majority
> get done.

Sounds good. I'm sure Android folks will speak up in case they require 
more efficient scanning.

> 
>>
>> --
>> Cheers,
>>
>> David / dhildenb
>>
> 
> Great minds think alike though ;) as soon as I saw this I did think about
> extending it, but seems I mistakenly dismissed for uffd reasons.
We should probably look into cleaning up + improving the documentation 
around the pagemap scan feature at some point. Well, something for 
another day :)

-- 
Cheers,

David / dhildenb