linux-kernel - Re: [PATCH 0/4] mm: permit guard regions for file-backed/shmem mappings

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Message-ID: <48ffe442-5015-44fe-bbd6-708ba8500505@redhat.com>
Date: Tue, 25 Feb 2025 17:48:17 +0100
From: David Hildenbrand <david@...hat.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Suren Baghdasaryan <surenb@...gle.com>,
 "Liam R . Howlett" <Liam.Howlett@...cle.com>,
 Matthew Wilcox <willy@...radead.org>, "Paul E . McKenney"
 <paulmck@...nel.org>, Jann Horn <jannh@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, Shuah Khan <shuah@...nel.org>,
 linux-kselftest@...r.kernel.org, linux-api@...r.kernel.org,
 John Hubbard <jhubbard@...dia.com>, Juan Yescas <jyescas@...gle.com>,
 Kalesh Singh <kaleshsingh@...gle.com>
Subject: Re: [PATCH 0/4] mm: permit guard regions for file-backed/shmem
 mappings

>> As for compatibility with VM_LOCKONFAULT, do we need a new
>> MADV_GUARD_INSTALL_LOCKED or can we say MADV_GUARD_INSTALL is new enough
>> that it can be just retrofitted (like you retrofit file backed mappings)?
>> AFAIU the only risk would be breaking somebody that already relies on a
>> failure for VM_LOCKONFAULT, and it's unlikely there's such a somebody now.
>>
>>
> 
> Hmm yeah I suppose. I guess just to be consistent with the other _LOCKED
> variants? (which seem to be... undocumented at least in man pages :P, and yes I
> realise this is me semi-volunteering to do that obviously...).
> 
> But on the other hand, we could also expand this if you and I see also Dave feel
> this makes sense and wouldn't be confusing.

Just my 2 cents: one thing that came to mind: an existing library would 
have to be updated to use the _LOCKED variant if the app would be using 
mlockall(future), which is a bit unfortunate -- and if it could be 
avoided, it would be great.

But yeah, devil is in the detail ...

-- 
Cheers,

David / dhildenb