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Wed, 27 Aug 2025 18:03:10 GMT Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E28EB5805D; Wed, 27 Aug 2025 18:03:09 +0000 (GMT) Received: from smtpav06.dal12v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E545658043; Wed, 27 Aug 2025 18:03:06 +0000 (GMT) Received: from [9.124.214.234] (unknown [9.124.214.234]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 27 Aug 2025 18:03:06 +0000 (GMT) Message-ID: Date: Wed, 27 Aug 2025 23:33:05 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] mm/ksm: Reset KSM counters in mm_struct during fork To: David Hildenbrand , Andrew Morton Cc: Ritesh Harjani , Xu Xin , Chengming Zhou , Wei Yang , Aboorva Devarajan , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <2e662107e01417bf9af23bc7f52863cd538419be.1756211338.git.donettom@linux.ibm.com> <59fef25c-6559-4fb3-8810-c2a7dd36b95a@redhat.com> Content-Language: en-US From: Donet Tom In-Reply-To: <59fef25c-6559-4fb3-8810-c2a7dd36b95a@redhat.com> Content-Type: text/plain; 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This results in >> incorrect accounting, since the child has not performed any >> KSM page merging. > > So, the situation is that our child process maps these pages, but it > does not have any stable rmap items corresponding to these pages. Yes > > rmap_walk_ksm() spells that case out. > > Can you clarify that in the description here, and how both stats > correspond to rmap items? Sure I will add it in next version. > > What is the effective result of this misacounting? I assume only a > higher number than expected. > Yes the number will be higher than expected. > > >> >> To fix this, reset these counters to 0 in the newly created >> `mm_struct` during fork. This ensures that KSM statistics >> remain accurate and only reflect the activity of each process. >> > > Fixes? CC stable? I will add it in next version. > >> Signed-off-by: Donet Tom >> --- >>   include/linux/ksm.h | 6 +++++- >>   1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/include/linux/ksm.h b/include/linux/ksm.h >> index 22e67ca7cba3..61b8892c632b 100644 >> --- a/include/linux/ksm.h >> +++ b/include/linux/ksm.h >> @@ -56,8 +56,12 @@ static inline long mm_ksm_zero_pages(struct >> mm_struct *mm) >>   static inline void ksm_fork(struct mm_struct *mm, struct mm_struct >> *oldmm) >>   { >>       /* Adding mm to ksm is best effort on fork. */ >> -    if (mm_flags_test(MMF_VM_MERGEABLE, oldmm)) >> +    if (mm_flags_test(MMF_VM_MERGEABLE, oldmm)) { >> +        mm->ksm_merging_pages = 0; >> +        mm->ksm_rmap_items = 0; >> +        atomic_long_set(&mm->ksm_zero_pages, 0); >>           __ksm_enter(mm); >> +    } >>   } >>     static inline int ksm_execve(struct mm_struct *mm) > >