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(p200300d82f0a7f00fad73bc9069d031f.dip0.t-ipconnect.de. [2003:d8:2f0a:7f00:fad7:3bc9:69d:31f]) by smtp.gmail.com with ESMTPSA id e3sm21662130wra.15.2021.07.19.13.47.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Jul 2021 13:47:46 -0700 (PDT) To: Peter Collingbourne , John Hubbard , Matthew Wilcox , "Kirill A . Shutemov" , Andrew Morton , Catalin Marinas , Evgenii Stepanov Cc: Jann Horn , Linux ARM , linux-mm@kvack.org, kernel test robot , Linux API , linux-doc@vger.kernel.org References: <20210619092002.1791322-1-pcc@google.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v4] mm: introduce reference pages Message-ID: <3268d400-7435-f038-a1a1-f476adb03845@redhat.com> Date: Mon, 19 Jul 2021 22:47:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210619092002.1791322-1-pcc@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=gFkHjFyb; spf=none (imf30.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam05 X-Stat-Signature: zh6ubbaqf59rcjd7n9jqci1z3ijuckf5 X-Rspamd-Queue-Id: D5482E003962 X-HE-Tag: 1626727669-694480 Content-Transfer-Encoding: quoted-printable 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: > +SYSCALL_DEFINE2(refpage_create, const void *__user, content, unsigned = long, > + flags) > +{ > + unsigned long content_addr =3D (unsigned long)content; > + struct page *userpage; > + struct refpage_private_data *private_data; > + int fd; > + > + if (flags !=3D 0) > + return -EINVAL; > + > + if ((content_addr & (PAGE_SIZE - 1)) !=3D 0 || > + get_user_pages(content_addr, 1, 0, &userpage, 0) !=3D 1) > + return -EFAULT; > + > + private_data =3D kzalloc(sizeof(struct refpage_private_data), GFP_KER= NEL); > + if (!private_data) { > + put_page(userpage); > + return -ENOMEM; > + } > + > + private_data->refpage =3D alloc_page(GFP_KERNEL); > + if (!private_data->refpage) { > + kfree(private_data); > + put_page(userpage); > + return -ENOMEM; > + } > + > + copy_highpage(private_data->refpage, userpage); > + arch_prep_refpage_private_data(private_data); > + put_page(userpage); > + > + fd =3D anon_inode_getfd("[refpage]", &refpage_file_operations, > + private_data, O_RDONLY | O_CLOEXEC); > + if (fd < 0) > + put_refpage_private_data(private_data); > + > + return fd; > +} >=20 Hi, some questions: 1. is there any upper limit or can a simple process effectively flood=20 the system with alloc_page(GFP_KERNEL)? (does ulimit -n apply or is it=20 /proc/sys/fs/file-max) 2. Shouldn't there be a GFP_ACCOUNT or am I missing something important? 3. How does this interact with MADV_DONTNEED? I assume we'll be able to=20 zap the mapped refpage and on refault, we'll map in the refpage again,=20 correct? --=20 Thanks, David / dhildenb