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[2003:cb:c717:6a00:e38f:c852:dc11:9146]) by smtp.gmail.com with ESMTPSA id w9-20020a05600c474900b003f17e37ce60sm8676540wmo.47.2023.04.21.09.52.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Apr 2023 09:52:15 -0700 (PDT) Message-ID: <14d89518-0c11-7bfb-0c72-329a834ba1a1@redhat.com> Date: Fri, 21 Apr 2023 18:52:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 To: Stefan Roesch Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Rik van Riel , Johannes Weiner , Michal Hocko , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Sven Schnelle , Shuah Khan References: <20230418051342.1919757-1-shr@devkernel.io> <20230418152849.505124-1-david@redhat.com> <20230418152849.505124-4-david@redhat.com> Content-Language: en-US From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [...] >> 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. >> */ >> - clear_bit(MMF_VM_MERGE_ANY, &mm->flags); >> - >> - for_each_vma(vmi, vma) { >> - /* Copy vm_flags to avoid partial modifications in ksm_madvise */ >> - vm_flags = vma->vm_flags; >> - ret = ksm_madvise(vma, vma->vm_start, vma->vm_end, >> - MADV_UNMERGEABLE, &vm_flags); >> - if (ret) >> - return ret; >> - vm_flags_reset(vma, vm_flags); >> - } >> - mm->def_flags &= ~VM_MERGEABLE; >> > Hi Stefan, > This clears the def_flags struct member, however, in ksm_disable() we > clear the __flags struct member. Is this a problem? The patch description contains a comment regarding def_flags: "The existing "mm->def_flags &= ~VM_MERGEABLE;" was essentially a NOP and can be dropped, because def_flags should never include VM_MERGEABLE." We keep clearing the MADV_UNMERGEABLE flag from MADV_UNMERGEABLE. In the old code, ksm_madvise() would have cleared it from local vm_flags and vm_flags_reset() would have modified vma->vm_flags. Now we clear it directly via vm_flags_clear(vma, VM_MERGEABLE); Long story short, the mm->def_flags code as wrong and most probably copied from thp_split_mm() where we do: mm->def_flags |= VM_NOHUGEPAGE; Which makes more sense. Thanks! -- Thanks, David / dhildenb