linux-kernel - Re: [PATCH v2 2/2] mm: shmem: disallow hugepages if the system-wide shmem THP sysfs settings are disabled

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Message-ID: <b455db10-f129-4603-a087-43a1b52ff09c@lucifer.local>
Date: Sat, 7 Jun 2025 13:17:05 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, david@...hat.com,
        Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
        dev.jain@....com, ziy@...dia.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm: shmem: disallow hugepages if the system-wide
 shmem THP sysfs settings are disabled

On Sat, Jun 07, 2025 at 01:14:41PM +0100, Lorenzo Stoakes wrote:
> On Thu, Jun 05, 2025 at 04:00:59PM +0800, Baolin Wang wrote:
[snip]
> >
> > Another rule for madvise, referring to David's suggestion: “allowing for collapsing
> > in a VM without VM_HUGEPAGE in the "madvise" mode would be fine".
>
> Hm I'm not sure if this is enforced is it? I may have missed something here
> however.

Oh right actually I think it is implicitly - if TVA_ENFORCE_SYSFS is not
specified in tva_flags, then we don't bother applying an madvise filter at all
anyway, and we account for that in our 'enabled' check in
thp_vma_allowable_orders().

But I don't think this patch changes anything, I actually _think_ we can just
drop this one.

[snip]