From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C6702421886 for ; Mon, 29 Jun 2026 14:39:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782743996; cv=none; b=LOMiHiE6fX1N4vqIMRCV4F6nWXUa6ddyoRlGGIJuZmUkxsbWtG1i7/QA36F9Ov3eRfetp3blMd1CzG2vIHFBFmHuGG5RFPXYwtzqamyFCqVAInLXURr2TCcPZKer3soUPkYU5g/3FWZ+tyq9R6DTmOo5Bg2ihhjQfWY769BAG+E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782743996; c=relaxed/simple; bh=1xk988xnnA8DBR4TtZ1NI1PQN4mhPSDUka+mCfMbEG0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=G0HwnQlbBTnU/n6eQzVQ3YHNZC8TFjDUo/7vXTOQGX2sTWXC7CcET9Z/TtH4SYX05Tqp4LJC/1hLl3HQOenLjplFr9SQ3moKfGWeibmQ5RfPzgmyeOMwG1s6Gqgyo7WRQa/3MuHT65DsL5z5aTvyW2ZSBenipyOn/wWA1hdHz18= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TOeIjCfo; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TOeIjCfo" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB0DE1F00A3E; Mon, 29 Jun 2026 14:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782743994; bh=DuMKsEYZ05nT54sTSWEYfjRA4P6TcC2zt7zo2qBxmsg=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=TOeIjCfo7zMwju0FALvWyC88HY2iC6CSLAq1JSqWnQVPM56LbgIOLWw8ZJ0QjD/Aw ozj4+rV5s0LPKS9cLaVzm4p4LzDe0sF4tCQfs9InvJgTGjzJ0YmxKImfnnhIqZZ8HE JVfKMA00m3ibwyDTuIffRXNts75e4qXrgb1c5kvObwIIvwfLnZRwS0x+NMMXjTwATy qYLFxu10DJrCQwvT1ghLjXlFES2/a4LNlLvyTXbfiskkKlr3wPORTGmJfTq1FL4qzJ 7H2t75310lRZtbCuXuYXoQ0l384A/TjR855SDyWmmsLLOkt+wwoCHxIik8SmISMtpL xcOtdxOD+t7lQ== Message-ID: <9fe5173c-4beb-42fe-8f7e-385c609f899f@kernel.org> Date: Mon, 29 Jun 2026 16:39:49 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] mm/huge_memory: add page->private check back in __split_folio_to_order() Content-Language: en-US To: Zi Yan , Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , David Hildenbrand , Lorenzo Stoakes , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Mike Rapoport Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260628-keep-subpage-private-zero-at-free-v1-0-f4ce3930d10f@nvidia.com> <20260628-keep-subpage-private-zero-at-free-v1-2-f4ce3930d10f@nvidia.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260628-keep-subpage-private-zero-at-free-v1-2-f4ce3930d10f@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/29/26 04:56, Zi Yan wrote: > page->private should not be set in tail pages. Commit 4265d67e405a > ("mm/migrate_device: add THP splitting during migration") removed it > without a proper reason. Add it back. > > Signed-off-by: Zi Yan > --- > mm/huge_memory.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 2bccb0a53a0a..037d67fbec6e 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3594,6 +3594,16 @@ static void __split_folio_to_order(struct folio *folio, int old_order, > new_folio->mapping = folio->mapping; > new_folio->index = folio->index + i; > > + /* > + * page->private should not be set in tail pages. Fix up and warn once > + * if private is unexpectedly set. Do it before swap.val assignment > + * since private overlaps with swap.val. > + */ > + if (unlikely(new_folio->private)) { > + VM_WARN_ON_ONCE_PAGE(true, new_head); > + new_folio->private = NULL; > + } The unconditional warning means this is not expected to happen. In that case it's odd to check and fixup always, but only warn with CONFIG_DEBUG_VM. If we are reasonably sure the current code is OK, and only want to catch new mistakes in development, we could just VM_WARN_ON_ONCE_PAGE() without fixup. If we are paranoid, leave it as it is, but drop the "VM_" ? > + > if (folio_test_swapcache(folio)) > new_folio->swap.val = folio->swap.val + i; > >