linux-kernel - Re: [PATCH v3 5/6] selftests: prctl: introduce tests for disabling THPs completely

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Message-ID: <2c795230-5885-4a1a-a0f9-c8352b9e7738@gmail.com>
Date: Tue, 5 Aug 2025 13:13:49 +0100
From: Usama Arif <usamaarif642@...il.com>
To: David Hildenbrand <david@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc: 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, ziy@...dia.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,
 Donet Tom <donettom@...ux.ibm.com>
Subject: Re: [PATCH v3 5/6] selftests: prctl: introduce tests for disabling
 THPs completely



On 05/08/2025 11:30, David Hildenbrand wrote:
> On 04.08.25 17:40, Usama Arif wrote:
>> The test will set the global system THP setting to never, madvise
>> or always depending on the fixture variant and the 2M setting to
>> inherit before it starts (and reset to original at teardown).
>>
>> This tests if the process can:
>> - successfully set and get the policy to disable THPs completely.
>> - never get a hugepage when the THPs are completely disabled
>>    with the prctl, including with MADV_HUGE and MADV_COLLAPSE.
>> - successfully reset the policy of the process.
>> - after reset, only get hugepages with:
>>    - MADV_COLLAPSE when policy is set to never.
>>    - MADV_HUGE and MADV_COLLAPSE when policy is set to madvise.
>>    - always when policy is set to "always".
>> - repeat the above tests in a forked process to make sure
>>    the policy is carried across forks.
>>
>> Signed-off-by: Usama Arif <usamaarif642@...il.com>
>> ---
>>   tools/testing/selftests/mm/.gitignore         |   1 +
>>   tools/testing/selftests/mm/Makefile           |   1 +
>>   .../testing/selftests/mm/prctl_thp_disable.c  | 173 ++++++++++++++++++
>>   tools/testing/selftests/mm/thp_settings.c     |   9 +-
>>   tools/testing/selftests/mm/thp_settings.h     |   1 +
>>   5 files changed, 184 insertions(+), 1 deletion(-)
>>   create mode 100644 tools/testing/selftests/mm/prctl_thp_disable.c
>>
>> diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
>> index e7b23a8a05fe..eb023ea857b3 100644
>> --- a/tools/testing/selftests/mm/.gitignore
>> +++ b/tools/testing/selftests/mm/.gitignore
>> @@ -58,3 +58,4 @@ pkey_sighandler_tests_32
>>   pkey_sighandler_tests_64
>>   guard-regions
>>   merge
>> +prctl_thp_disable
>> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
>> index d13b3cef2a2b..2bb8d3ebc17c 100644
>> --- a/tools/testing/selftests/mm/Makefile
>> +++ b/tools/testing/selftests/mm/Makefile
>> @@ -86,6 +86,7 @@ TEST_GEN_FILES += on-fault-limit
>>   TEST_GEN_FILES += pagemap_ioctl
>>   TEST_GEN_FILES += pfnmap
>>   TEST_GEN_FILES += process_madv
>> +TEST_GEN_FILES += prctl_thp_disable
>>   TEST_GEN_FILES += thuge-gen
>>   TEST_GEN_FILES += transhuge-stress
>>   TEST_GEN_FILES += uffd-stress
>> diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c
>> new file mode 100644
>> index 000000000000..ef150180daf4
>> --- /dev/null
>> +++ b/tools/testing/selftests/mm/prctl_thp_disable.c
>> @@ -0,0 +1,173 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Basic tests for PR_GET/SET_THP_DISABLE prctl calls
>> + *
>> + * Author(s): Usama Arif <usamaarif642@...il.com>
>> + */
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +#include <string.h>
>> +#include <unistd.h>
>> +#include <sys/mman.h>
>> +#include <sys/prctl.h>
>> +#include <sys/wait.h>
>> +
>> +#include "../kselftest_harness.h"
>> +#include "thp_settings.h"
>> +#include "vm_util.h"
>> +
>> +static int sz2ord(size_t size, size_t pagesize)
>> +{
>> +    return __builtin_ctzll(size / pagesize);
>> +}
> 
> Note: We have this helper duplicated elsewhere (e.g., cow.c).
> 
> See [1] how we're going to clean it up.
> 
> Not sure how to resolve this. Probably, which series lands first in mm-unstable should clean it up.
> 
> I would assume that Donet's series would go in first, such that you can just reuse the helper from vm_utils.h
> 
> [1] https://lkml.kernel.org/r/20250804090410.of5xwrlker665bdp@master
> 
> 
> Nothing else jumped at me
> 
> Acked-by: David Hildenbrand <david@...hat.com>
> 

Thanks!

I will wait a few days and see if it has made it into mm-new and rebase and send the next revision.