linux-kernel - Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are disabled

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Message-ID: <3b6db0c3-aef3-4a21-a154-6aafd639dbc7@lucifer.local>
Date: Wed, 25 Jun 2025 08:42:16 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Hugh Dickins <hughd@...gle.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
        ziy@...dia.com, Liam.Howlett@...cle.com, npache@...hat.com,
        ryan.roberts@....com, dev.jain@....com, baohua@...nel.org,
        zokeefe@...gle.com, shy828301@...il.com, usamaarif642@...il.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/2] fix MADV_COLLAPSE issue if THP settings are
 disabled

On Wed, Jun 25, 2025 at 09:36:53AM +0200, David Hildenbrand wrote:
> On 25.06.25 09:30, Lorenzo Stoakes wrote:
> > I _guarantee_ you that's what nearly everybody except a handful of people will
> > expect.
>
> I know, See my other mail, the problem is rather if there is no somebody
> relying on never+MADV_COLLAPSE from doing the MADV_COLLAPSE-documented
> thing.
>
> It's a mess.

Well now we have an almost philosophical debate - we have different sets of
users, 99% of whom believe the uAPI is X, and 1% of whom believe it is Y.

Now what is the uAPI? What is 'breaking userspace'? :)

Temptation to cc Linus here ;)

>
> (I have the suspicion that Hugh might know of such a user :) )

Speak up Hugh we're all friends here haha ;)

I mean if this really is a problem for real users then I'll concede the point.

Let me reply on other thread...

> > I really really dislike this. 'Deny' is weaker than 'never'. And now we have to
> > add even more complexity to the thing.
>
> See my other mail, for shmem_enabled "deny" is stronger than "never", lol.

OK so we're past the throwing up stage, can I cry now? :P