linux-kernel - Re: [PATCH v5 6/7] selftests: prctl: introduce tests for disabling THPs completely

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Message-ID: <abe39fc3-37a3-416d-b868-345f4e577427@gmail.com>
Date: Fri, 5 Sep 2025 20:40:25 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Mark Brown <broonie@...nel.org>, Zi Yan <ziy@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, david@...hat.com,
 linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, corbet@....net,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, hannes@...xchg.org,
 baohua@...nel.org, shakeel.butt@...ux.dev, riel@...riel.com,
 laoar.shao@...il.com, dev.jain@....com, baolin.wang@...ux.alibaba.com,
 npache@...hat.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 ryan.roberts@....com, vbabka@...e.cz, jannh@...gle.com,
 Arnd Bergmann <arnd@...db.de>, sj@...nel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, kernel-team@...a.com, Aishwarya.TCV@....com
Subject: Re: [PATCH v5 6/7] selftests: prctl: introduce tests for disabling
 THPs completely



On 05/09/2025 19:02, Mark Brown wrote:
> On Fri, Sep 05, 2025 at 01:55:53PM -0400, Zi Yan wrote:
>> On 5 Sep 2025, at 13:43, Mark Brown wrote:
> 
>>> but the header there is getting ignored AFAICT.  Probably the problem is
>>> fairly obvious and I'm just being slow - I'm not quite 100% at the
>>> minute.
> 
>> prctl_thp_disable.c uses “#include <sys/mman.h>” but asm-generic/mman-common.h
>> is included in asm/mman.h. And sys/mman.h gets MADV_COLLAPSE from
>> bits/mman-linux.h. Maybe that is why?
> 
> Ah, of course - if glibc is reproducing the kernel definitions rather
> than including the kernel headers to get them then that'd do it.
> Probably the test needs to locally define the new MADV_COLLAPSE for
> glibc compatibility, IME trying to directly include the kernel headers
> when glibc doesn't normally use them tends to blow up on you sooner or
> later.
> 
> I knew it'd be something simple, thanks.

Hi Mark,

Thanks for raising this. I think doing 

diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c
index 89ed0d7db1c16..0afcdbad94f3d 100644
--- a/tools/testing/selftests/mm/prctl_thp_disable.c
+++ b/tools/testing/selftests/mm/prctl_thp_disable.c
@@ -9,6 +9,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <sys/mman.h>
+#include <linux/mman.h>
 #include <sys/prctl.h>
 #include <sys/wait.h>


should fix this issue?

Thanks
Usama