linux-kernel - Re: [PATCH 1/6] mm/selftests: Fix virtual_address

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Message-ID: <79bdd993-0e9c-4d7d-b42c-4b5750eff140@lucifer.local>
Date: Wed, 18 Jun 2025 12:37:29 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Dev Jain <dev.jain@....com>
Cc: Aboorva Devarajan <aboorvad@...ux.ibm.com>, akpm@...ux-foundation.org,
        Liam.Howlett@...cle.com, shuah@...nel.org, pfalcato@...e.de,
        david@...hat.com, ziy@...dia.com, baolin.wang@...ux.alibaba.com,
        npache@...hat.com, ryan.roberts@....com, baohua@...nel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, donettom@...ux.ibm.com,
        ritesh.list@...il.com
Subject: Re: [PATCH 1/6] mm/selftests: Fix virtual_address_range test issues.

On Wed, Jun 18, 2025 at 04:58:56PM +0530, Dev Jain wrote:
>
> MAP_CHUNK_SIZE was chosen randomly. Good to see it translates into something logical : )
>
> So I guess I am correct, if we can find two VMAs (except at the edge of the high addr boundary)
> with a gap of greater than MAP_CHUNK_SIZE then there is a bug in mmap().

No haha, not at all!! Firstly fixed addressed override a lot of this, secondly
the 256 page gap (which is configurable btw) is only applicable for mappings
below a stack (in stack grow down arch).

This assumption is totally incorrect, sorry. I'd suggest making assertions about
this is really not all that useful, as things vary by arch and kernel
configuration.