From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 D7B351482F2 for ; Thu, 19 Dec 2024 16:52:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734627128; cv=none; b=PNUZDheZz2EbKETk8E/HZdJy0p+8OAHGAWBXfNQMOgbSQSvAmIme5clFZDpBZhL3cK6Uutt8pBR7JF6OSOKaSRLM/GV5/jTNzBRqbSS5JMcA7O8p+OW+X8QiF3Yabaj07OYmXJp2VSD4XTpsuq84BFJ6DepZpIemsnhWK1auBPA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734627128; c=relaxed/simple; bh=WyTgacPIQOdlvZYSa5vcrA+ZzX4kXxw4Gnm1kNwaOe8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=vGOfbKrFkeLtnQAEgqO9eeRtM04S6YSy590ja0USOHQ20HcmyewrFQQ+5DOxLKr0PtSYhsHqH51KVOabqWFimDKSK4+vYGfF7x5dA7GcuFtg+98qHVDQpKCwy2n1/dUzBNz4kf6j7PYfRFVfPNo3VOjruJwRT2XZrIb7JYZZC70= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=tJ+ZI58m; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="tJ+ZI58m" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=g9BcSRrxUykMMVWj5F8KcTDiGGo2F5oqCWeRlheeGGg=; b=tJ+ZI58mvRmrTmN7x4Gn8NCaZU aZkT5poG1xFZfz25ezJSCIsiuAiAL1Oiy5jDhYklV1RpcN+ZjDnwrfyLyFEToD3QJps+kRl22GH8V Om4v5+zoa+kIeq04ExYu4O8dv86iRjTc2k+KD/5jD3ix2upX5pKe+LPEBMi9lDLSD+qqfIwnpv60U dTZJYUgyLEfIJbV8PbQyydSSmXg/Mo06GFQ9qzUgtNezXlxRvPrAHQ0ZIViqXLBv7LBbMZXaTVQzS 93X+rHw0bsnFOgWT240xbgJSnXd43Ns1Xvv9aFl2wVPNvuQvFLbzafJfZGlXYiZsvbOZAgau7NOU/ 7q50qrpQ==; Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tOJkq-00000004PtZ-2XWa; Thu, 19 Dec 2024 16:52:04 +0000 Date: Thu, 19 Dec 2024 16:52:04 +0000 From: Matthew Wilcox To: David Hildenbrand Cc: Claudio Imbrenda , linux-mm@kvack.org, linux-s390@vger.kernel.org Subject: Re: [PATCH 0/2] s390: Remove uses of page->index Message-ID: References: <20241219162252.1025317-1-willy@infradead.org> <9d4efc2e-56d9-4786-9ccb-ecd15f34f3e7@redhat.com> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9d4efc2e-56d9-4786-9ccb-ecd15f34f3e7@redhat.com> On Thu, Dec 19, 2024 at 05:33:32PM +0100, David Hildenbrand wrote: > On 19.12.24 17:22, Matthew Wilcox (Oracle) wrote: > > These two patches compile ... I can promise nothing more than that. > > > > David suggested to me that the gmap code really should be using ptdesc, > > and I think I agree with him. The vsie code looks quite different > > and probably shouldn't be using a ptdesc, but we can use page->private > > instead of page->index. It's not yet clear to me if we'll ever manage > > to get rid of page->private. > > Just curious, does that mean that memdesc would always contain these > additional 8 bytes? Eventually we'll have a choice to make. 1. Shrink struct page to 8 bytes, but we'll need to allocate a 32 byte memdesc for all the current users of page->private 2. Shrink struct page to 16 bytes I genuinely don't know which will be better for the whole system. If you're asking because we can defer some of the mapcount work by using the 8 bytes of page->private to store mapcount, then yes, let's do that.