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([2a09:80c0:192:0:20af:34be:985b:b6c8]) by smtp.gmail.com with ESMTPSA id v13-20020adfe28d000000b0020375f27a5asm4109290wri.4.2022.03.17.05.32.49 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Mar 2022 05:32:49 -0700 (PDT) Message-ID: Date: Thu, 17 Mar 2022 13:32:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: [PATCH v2] mm: add access/dirty bit on numa page fault Content-Language: en-US To: Bibo Mao , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Anshuman Khandual References: <20220317065033.2635123-1-maobibo@loongson.cn> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220317065033.2635123-1-maobibo@loongson.cn> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17.03.22 07:50, Bibo Mao wrote: > On platforms like x86/arm which supports hw page walking, access > and dirty bit is set by hw, however on some platforms without > such hw functions, access and dirty bit is set by software in > next trap. > > During numa page fault, dirty bit can be added for old pte if > fail to migrate on write fault. And if it succeeds to migrate, > access bit can be added for migrated new pte, also dirty bit > can be added for write fault. > > Signed-off-by: Bibo Mao > --- > mm/memory.c | 21 ++++++++++++++++++++- > 1 file changed, 20 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index c125c4969913..65813bec9c06 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -4404,6 +4404,22 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) > if (migrate_misplaced_page(page, vma, target_nid)) { > page_nid = target_nid; > flags |= TNF_MIGRATED; > + > + /* > + * update pte entry with access bit, and dirty bit for > + * write fault > + */ > + spin_lock(vmf->ptl); Ehm, are you sure? We did a pte_unmap_unlock(), so you most certainly need a vmf->pte = pte_offset_map(vmf->pmd, vmf->address); Also, don't we need pte_same() checks before we do anything after dropping the PT lock? > + pte = *vmf->pte; > + pte = pte_mkyoung(pte); > + if (was_writable) { > + pte = pte_mkwrite(pte); > + if (vmf->flags & FAULT_FLAG_WRITE) > + pte = pte_mkdirty(pte); > + } > + set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte); > + update_mmu_cache(vma, vmf->address, vmf->pte); > + pte_unmap_unlock(vmf->pte, vmf->ptl); > } else { > flags |= TNF_MIGRATE_FAIL; > vmf->pte = pte_offset_map(vmf->pmd, vmf->address); > @@ -4427,8 +4443,11 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) > old_pte = ptep_modify_prot_start(vma, vmf->address, vmf->pte); > pte = pte_modify(old_pte, vma->vm_page_prot); > pte = pte_mkyoung(pte); > - if (was_writable) > + if (was_writable) { > pte = pte_mkwrite(pte); > + if (vmf->flags & FAULT_FLAG_WRITE) > + pte = pte_mkdirty(pte); > + } > ptep_modify_prot_commit(vma, vmf->address, vmf->pte, old_pte, pte); > update_mmu_cache(vma, vmf->address, vmf->pte); > pte_unmap_unlock(vmf->pte, vmf->ptl); -- Thanks, David / dhildenb