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Fri, 21 Apr 2023 14:27:54 -0400 (EDT) References: <20230418051342.1919757-1-shr@devkernel.io> <20230418152849.505124-1-david@redhat.com> <20230418152849.505124-4-david@redhat.com> <14d89518-0c11-7bfb-0c72-329a834ba1a1@redhat.com> User-agent: mu4e 1.10.1; emacs 28.2.50 From: Stefan Roesch To: David Hildenbrand 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 Subject: Re: [PATCH v1 3/3] mm/ksm: move disabling KSM from s390/gmap code to KSM code Date: Fri, 21 Apr 2023 11:27:23 -0700 In-reply-to: <14d89518-0c11-7bfb-0c72-329a834ba1a1@redhat.com> Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: sdbcofeyf1zft5anxt1m3o5fu45snq81 X-Rspamd-Queue-Id: 5F2DD1A001C X-HE-Tag: 1682101677-890953 X-HE-Meta: U2FsdGVkX1+lnT9TK/NfgZWvZN6DEsAx6UmLO5twsNOPlfVdlpaM+jOgk2KyqP/n14hY97baKLU6nZqwRht/NCNTAz4ve3CuUjbkFGsgq1phyHXN7TLYt7sM0a2u+tHugeejDmyKorFRxfo0VXoXMDba8h6X840YV6OuVlXhyerps59/ckp6xA10ADuCIeTqYuxE+p5YRuk8FU0o6DSSlczuaD7DFQSpd2Nwz/GRELMiIJgHNQyiqV1iBJKD0va/zGSh9DytCscraKIFEU3z3Su7a/yJWhIDdC1LNHyr9dEx8hWzKTwEgbeICR/3C1PabJYkPGaeYnmmRmfhMdHZdgI6I1M5vI6hTGvGlbMx03D3K0qgM3t0zYMp1aQn7BL1Zey7WqHYtghb95dFrbjNP8DxVy2lrqpPOs5Sl9YVt/1lBZld5fNQu3ElCIwVsXVM0kTsjId3EMdwCnhlo+GMqdOJ7ILmsQk6efLMjjS74G+d7ven1R/JbtONFeuvoExWyEn4x/E85U11YW8Imcd4da2dy2Zymt3uiMsRXLtTt7ov5vf19qMVACdoou3VVHcl/TwKinIh4HzC9ra54GfVw5kHuMNxCrfozMgaUPAbMNKIv4wzJNi7tP0AZMajQGVx7mfDf/iJBZyPMVbc35wShS96waNqK05y8HcEaSjq0G0X6JO+DWbm02NWxow2wWnO/FXziTbu81ESyHN70qy/Nya+eYbJyfvCz0pRQL/AVyx3MK6tG+bp+KI0PX056780cipE7XIjP8OSHMQv2V9WVX78TnjLv9kxjyi7rzC1IzxVuI4gyt4HU7HKsKhtCoLsHv+HCeTC3DtxjmS4t1BlFzp2wEno6rKr360QSzHm7DEd4pkN3aCGeQ6eJ/J5qkIjhM8QM+5qvyO0+gxXhocyfuPJt+13QGNhZ2Z5cvsa+DQTkWwcfc2WGDpe0lZ9cHd0FKvFxM/9Rogzjd5RcZh 3sUIOigH 2A+2nagnp19m7cGfywPBnw9t0Qfy3dmhgFkaDxrLeE4UIzFSfWQSQL50uBP9+OS60NTvKJOdxI+isXZNP0LaecE6FB8Lczh3GxKWv69PP+zU0cbsnozdVN66gc63risZiORGivSrnC1fw9mFthSFXuuJjuQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: David Hildenbrand writes: > [...] > >>> 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 for the explanation. Acked-by: Stefan Roesch