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To: Zi Yan Cc: "Kirill A. Shutemov" , Linux MM , Linux Kernel Mailing List , linux-kselftest@vger.kernel.org, "Kirill A . Shutemov" , Andrew Morton , Shuah Khan , John Hubbard , Sandipan Das , David Hildenbrand , Mika Penttila Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: mzzwkp5qyqudqoz46z5bwp9xbxwq7k89 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 65614401C84E Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf02; identity=mailfrom; envelope-from=""; helo=mail-ej1-f42.google.com; client-ip=209.85.218.42 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1615835625-864104 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 Mon, Mar 15, 2021 at 11:37 AM Zi Yan wrote: > > On 15 Mar 2021, at 8:07, Kirill A. Shutemov wrote: > > > On Thu, Mar 11, 2021 at 07:57:12PM -0500, Zi Yan wrote: > >> From: Zi Yan > >> > >> We do not have a direct user interface of splitting the compound page > >> backing a THP > > > > But we do. You expand it. > > > >> and there is no need unless we want to expose the THP > >> implementation details to users. Make /split_huge_pages accep= t > >> a new command to do that. > >> > >> By writing ",," to > >> /split_huge_pages, THPs within the given virtual address rang= e > >> from the process with the given pid are split. It is used to test > >> split_huge_page function. In addition, a selftest program is added to > >> tools/testing/selftests/vm to utilize the interface by splitting > >> PMD THPs and PTE-mapped THPs. > >> > > > > Okay, makes sense. > > > > But it doesn't cover non-mapped THPs. tmpfs may have file backed by THP > > that mapped nowhere. Do we want to cover this case too? > > Sure. It would be useful when large page in page cache too. I will send > v4 with tmpfs THP split. I will definitely need a review for it, since > I am not familiar with getting a page from a file path. We do have some APIs to return pages for a file range, i.e. find_get_page find_get_pages find_get_entries find_get_pages_range They all need address_space, so you need to convert file path to address_space before using them. The hole punch of tmpfs uses find_get_entries(), just check what shmem_undo_range() does. > > > Maybe have PID:,, and > > FILE:,, ? > > Or just check input[0] =3D=3D =E2=80=98/=E2=80=98 for file path input. > > > =E2=80=94 > Best Regards, > Yan Zi