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David Alan Gilbert" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1657646412; a=rsa-sha256; cv=none; b=FRl636n+prOfwXVsnxYsNcI7Ajs8rT8uIa7NwPwLDo9Sk/t1bGfDOa4c1YWgl+yo58ZoCS j4SydPz/d57fzFUf9/U0hls+7QCLEEiE4WMZhgLZYyleyXWMkkC9xEFSQZSG8m3hB63OzM N9SpcA+JVWAnFkbkAi9egWjftTpZuhE= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b="LKapj/7e"; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf21.hostedemail.com: domain of jthoughton@google.com designates 209.85.167.42 as permitted sender) smtp.mailfrom=jthoughton@google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1657646412; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ibrUHnlGz87syZWBzvYZCl2iDjwrLt5IxsZ/+T6H5Kk=; b=rzekkDcU/tbPX5AM0UQi3GsnjbXrw5iQfkqvffdn9ycEb9Xz8IHHLZ5khYgj2RJoGmynwO T+hGFgvLCCabQJCqVvGp+2cxKiW3C4UJXaXUjYLap8gTb10sMJlDUv2VhPkdHpqMI0ZTCN 1p7LXfwB5wTxxGHmC3e8VgG/mweN8JE= Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b="LKapj/7e"; dmarc=pass (policy=reject) header.from=google.com; spf=pass (imf21.hostedemail.com: domain of jthoughton@google.com designates 209.85.167.42 as permitted sender) smtp.mailfrom=jthoughton@google.com X-Rspam-User: X-Stat-Signature: bogifwngeqzbzg1r7oihkzieiwxfhhqr X-Rspamd-Queue-Id: 803E11C007A X-Rspamd-Server: rspam08 X-HE-Tag: 1657646412-203472 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, Jul 11, 2022 at 4:41 PM Mike Kravetz wrote: > > On 06/24/22 17:36, James Houghton wrote: > > This allows fork() to work with high-granularity mappings. The page > > table structure is copied such that partially mapped regions will remain > > partially mapped in the same way for the new process. > > > > Signed-off-by: James Houghton > > --- > > mm/hugetlb.c | 74 +++++++++++++++++++++++++++++++++++++++++----------- > > 1 file changed, 59 insertions(+), 15 deletions(-) > > FYI - > With https://lore.kernel.org/linux-mm/20220621235620.291305-5-mike.kravetz@oracle.com/ > copy_hugetlb_page_range() should never be called for shared mappings. > Since HGM only works on shared mappings, code in this patch will never > be executed. > > I have a TODO to remove shared mapping support from copy_hugetlb_page_range. Thanks Mike. If I understand things correctly, it seems like I don't have to do anything to support fork() then; we just don't copy the page table structure from the old VMA to the new one. That is, as opposed to having the same bits of the old VMA being mapped in the new one, the new VMA will have an empty page table. This would slightly change how userfaultfd's behavior on the new VMA, but that seems fine to me. - James > -- > Mike Kravetz