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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id o2sm4977837qkk.42.2020.09.26.16.23.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 26 Sep 2020 16:23:35 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kMJXT-001Tdk-C5; Sat, 26 Sep 2020 20:23:35 -0300 Date: Sat, 26 Sep 2020 20:23:35 -0300 From: Jason Gunthorpe To: Peter Xu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, John Hubbard , Andrew Morton , Christoph Hellwig , Yang Shi , Oleg Nesterov , Kirill Tkhai , Kirill Shutemov , Hugh Dickins , Jann Horn , Linus Torvalds , Michal Hocko , Jan Kara , Andrea Arcangeli , Leon Romanovsky Subject: Re: [PATCH v2 3/4] mm: Do early cow for pinned pages during fork() for ptes Message-ID: <20200926232335.GA348793@ziepe.ca> References: <20200925222600.6832-1-peterx@redhat.com> <20200925222600.6832-4-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200925222600.6832-4-peterx@redhat.com> 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: On Fri, Sep 25, 2020 at 06:25:59PM -0400, Peter Xu wrote: > -static inline void > +/* > + * Copy one pte. Returns 0 if succeeded, or -EAGAIN if one preallocated page > + * is required to copy this pte. > + */ > +static inline int > copy_present_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, > pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *vma, > - unsigned long addr, int *rss) > + struct vm_area_struct *new, > + unsigned long addr, int *rss, struct page **prealloc) > { > unsigned long vm_flags = vma->vm_flags; > pte_t pte = *src_pte; > struct page *page; > > + page = vm_normal_page(vma, addr, pte); > + if (page) { > + if (is_cow_mapping(vm_flags)) { > + bool is_write = pte_write(pte); Very minor, but I liked the readability to put this chunk in a function 'copy_normal_page' with the src/dst naming > + > + /* > + * We have a prealloc page, all good! Take it > + * over and copy the page & arm it. > + */ > + *prealloc = NULL; > + copy_user_highpage(new_page, page, addr, vma); > + __SetPageUptodate(new_page); > + pte = mk_pte(new_page, new->vm_page_prot); > + pte = pte_sw_mkyoung(pte); Linus's version doesn't do pte_sw_mkyoung(), but looks OK to have it > + pte = maybe_mkwrite(pte_mkdirty(pte), new); maybe_mkwrite() was not in Linus's version, but is in wp_page_copy(). It seemed like mk_pte() should set the proper write bit already from the vm_page_prot? Perhaps this is harmless but redundant? > + page_add_new_anon_rmap(new_page, new, addr, false); > + rss[mm_counter(new_page)]++; > + set_pte_at(dst_mm, addr, dst_pte, pte); Linus's patch had a lru_cache_add_inactive_or_unevictable() here, like wp_page_copy() Didn't think of anything profound to say, looks good thanks! I'll forward this for testing as well, there are some holidays next week so I may have been optimistic to think by Monday. Jason