linux-kernel - Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code

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Date:   Wed, 19 Apr 2023 13:40:18 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Janosch Frank <frankja@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-s390@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stefan Roesch <shr@...kernel.io>,
        Rik van Riel <riel@...riel.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to
 KSM code

On 19.04.23 13:39, Janosch Frank wrote:
> On 4/18/23 17:28, David Hildenbrand wrote:
>> Let's factor out actual disabling of KSM. The existing
>> "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped,
>> because def_flags should never include VM_MERGEABLE. Note that we don't
>> currently prevent re-enabling KSM.
>>
>> This should now be faster in case KSM was never enabled, because we only
>> conditionally iterate all VMAs. Further, it certainly looks cleaner.
>>
>> Signed-off-by: David Hildenbrand <david@...hat.com>
>> ---
>>    arch/s390/mm/gmap.c | 20 +-------------------
>>    include/linux/ksm.h |  6 ++++++
>>    mm/ksm.c            | 11 +++++++++++
>>    3 files changed, 18 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
>> index 0949811761e6..dfe905c7bd8e 100644
>> --- a/arch/s390/mm/gmap.c
>> +++ b/arch/s390/mm/gmap.c
>> @@ -2585,30 +2585,12 @@ EXPORT_SYMBOL_GPL(s390_enable_sie);
>>    
>>    int gmap_mark_unmergeable(void)
>>    {
>> -	struct mm_struct *mm = current->mm;
>> -	struct vm_area_struct *vma;
>> -	unsigned long vm_flags;
>> -	int ret;
>> -	VMA_ITERATOR(vmi, mm, 0);
>> -
>>    	/*
>>    	 * Make sure to disable KSM (if enabled for the whole process or
>>    	 * individual VMAs). Note that nothing currently hinders user space
>>    	 * from re-enabling it.
>>    	 */
> 
> Is that still true?

Yes. We'd need another per-MM bit to stop it from getting re-enabled.

> 
> My KSM knowledge is nearly zero but from what I can see the patch looks
> ok to me:
> Acked-by: Janosch Frank <frankja@...ux.ibm.net>


Thanks!

-- 
Thanks,

David / dhildenb