linux-kernel - Re: [PATCH 00/16] mm: Introduce MAP_BELOW

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Message-ID: <fd1b8016-e73d-4535-9c67-579ab994351f@intel.com>
Date: Wed, 28 Aug 2024 11:29:56 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Charlie Jenkins <charlie@...osinc.com>, Arnd Bergmann <arnd@...db.de>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
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Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH 00/16] mm: Introduce MAP_BELOW_HINT

On 8/27/24 22:49, Charlie Jenkins wrote:
> Some applications rely on placing data in free bits addresses allocated
> by mmap. Various architectures (eg. x86, arm64, powerpc) restrict the
> address returned by mmap to be less than the maximum address space,
> unless the hint address is greater than this value.

Which applications are these, btw?

Is this the same crowd as the folks who are using the address tagging
features like X86_FEATURE_LAM?

Even if they are different, I also wonder if a per-mmap() thing
MAP_BELOW_HINT is really what we want.  Or should the applications
you're trying to service here use a similar mechanism to how LAM affects
the *whole* address space as opposed to an individual mmap().