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Thu, 20 Apr 2023 17:42:13 -0400 (EDT) References: <20230418051342.1919757-1-shr@devkernel.io> <20230418152849.505124-1-david@redhat.com> <20230418152849.505124-4-david@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: Thu, 20 Apr 2023 14:41:00 -0700 In-reply-to: <20230418152849.505124-4-david@redhat.com> Message-ID: MIME-Version: 1.0 Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 1804E4001E X-Stat-Signature: bqcecwz7h8tdzdsk6mkc7c6kxnxqtngq X-HE-Tag: 1682026937-35455 X-HE-Meta: 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 noqt6Fza /EaI1f/qwcMm2DWefTU02Waroti8GYIegQVXmmroZCJILmQBiliWQUVhmZxYCmVcXeEwmkSzX6mLLj59yivqbKrhod8MbfOgX410spMPWfyLxPuV6N56wo1/arFmT4WcRA9tLxmEE3RqIjvABi9FDaic/Eg== 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: > 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 > --- > 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. > */ > - 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; > This clears the def_flags struct member, however, in ksm_disable() we clear the __flags struct member. Is this a problem? > - return 0; > + return ksm_disable(current->mm); > } > EXPORT_SYMBOL_GPL(gmap_mark_unmergeable); > > diff --git a/include/linux/ksm.h b/include/linux/ksm.h > index 7108bc65dc2a..b3d8b7849e18 100644 > --- a/include/linux/ksm.h > +++ b/include/linux/ksm.h > @@ -22,6 +22,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start, > void ksm_add_vma(struct vm_area_struct *vma); > int ksm_enable_merge_any(struct mm_struct *mm); > int ksm_disable_merge_any(struct mm_struct *mm); > +int ksm_disable(struct mm_struct *mm); > > int __ksm_enter(struct mm_struct *mm); > void __ksm_exit(struct mm_struct *mm); > @@ -75,6 +76,11 @@ static inline void ksm_add_vma(struct vm_area_struct *vma) > { > } > > +static inline int ksm_disable(struct mm_struct *mm) > +{ > + return 0; > +} > + > static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) > { > return 0; > diff --git a/mm/ksm.c b/mm/ksm.c > index 813f7fbc1832..208311cbb019 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -2616,6 +2616,17 @@ int ksm_disable_merge_any(struct mm_struct *mm) > return 0; > } > > +int ksm_disable(struct mm_struct *mm) > +{ > + mmap_assert_write_locked(mm); > + > + if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) > + return 0; > + if (test_bit(MMF_VM_MERGE_ANY, &mm->flags)) > + return ksm_disable_merge_any(mm); > + return ksm_del_vmas(mm); > +} > + > int ksm_madvise(struct vm_area_struct *vma, unsigned long start, > unsigned long end, int advice, unsigned long *vm_flags) > {