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([2600:1700:5610:6e80::41]) by smtp.gmail.com with ESMTPSA id y11-20020a4ad64b000000b00333c9ad6eb8sm815835oos.21.2022.04.22.07.00.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Apr 2022 07:00:43 -0700 (PDT) Message-ID: <1f0f3254-31bd-5d09-6520-1897b3c5755b@redhat.com> Date: Fri, 22 Apr 2022 10:00:41 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [RFC 1/3] mm: change vma_is_anonymous to vma_is_private_anon Content-Language: en-US To: Matthew Wilcox Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Alexander Viro , Andrew Morton , Nicholas Piggin , Logan Gunthorpe , Hari Bathini , "Aneesh Kumar K.V" , Yang Shi , Miaohe Lin , William Kucharski , Hugh Dickins References: <20220421190533.1601879-1-npache@redhat.com> <20220421190533.1601879-2-npache@redhat.com> From: Nico Pache In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/21/22 15:28, Matthew Wilcox wrote: > On Thu, Apr 21, 2022 at 03:05:31PM -0400, Nico Pache wrote: >> The vma_is_anonymous function isn't fully indicative of what it checks. >> >> Without having full knowledge of the mmap process, one may incorrectly >> assume this covers all types of anonymous memory; which is not the case. > > Is your complaint that anonymous memory can also be found in file VMAs > that were mapped with MAP_PRIVATE? ie COWed pages? I should have been more descriptive in my commit msg about how I came to this conclusion. >From my understanding of the mmap process, a vma->vm_ops field is only NULL when mmapped as !file and !shared: if (file){ ... } else if (vm_flags & VM_SHARED) { //ANON SHARED error = shmem_zero_setup(vma); if (error) goto free_vma; } else { //ANON PRIVATE vma_set_anonymous(vma); //set vma->vm_ops= NULL } To me this means that the VMA is PRIVATE ANON memory. The vma_is_anonymous function returns true when vm_ops == NULL. So my intentions were to more accurately describe what we are checking for. I could be wrong though thats why I started with an RFC :) There could be some aspect of COW that I dont fully understand. It is not something I've looked into much. Cheers, -- Nico