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 DB7703A1A21 for ; Fri, 25 Sep 2026 07:15:15 +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=1790320516; cv=none; b=qwaWGX2GSQZB5bayucGOLb+n1m/DbDP+7h1DB8VV3F6zX8aBRxkLKU7v279JKMiFnKkBIzwE9mnVo8B6kRPO4DXNsqJYjH7CLWaOent9l6GClYMQ5NYbdcYlBYzlxC1xw5k2zZkiQ8K7rvPtI9sLYc4K5V3vWEn9a9yTNrGfhd8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790320516; c=relaxed/simple; bh=IIMlJ8/tiypATGIYJ0O2GjPc4AYhdtjMK3KtgqyfqYk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=cWFLrWCDPLhhCLg4PE1kx5wfPjsyrmgnVOCNUUaEv6FRmIPBqPiMSwV9GU9CAYGaPEcDWtP4nEabn/alxNm8Kj1gnPQrWUfUdRxzOUEXqBnvRi/7fu0fRZJ/DuE9A9R568PscPyGzRe2YSC2T4jbrU3y9mJ9koF9B0Rn2+ei7Kk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=K3W8lDCm; 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="K3W8lDCm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BA631F000FF; Fri, 25 Sep 2026 07:15:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790320515; bh=K7gdWsILDeGL2fq4hXJ9qNq6gT7AIFOxT+XzWAS6HA4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=K3W8lDCm6YecnNVEKENAO2Z6Sg7cT/3eLRojKTT6Z9zscAa/v/5cqGv3GNPCLAGEp 535X6IYjYQnPdQSkuW0jarjrIMu8TG3MAad+tPqdtJJd80EQSMeNM67ts1y4gFv9Mh 3shg6wfIiE7m9n6ku2qbiiPe+vdifcqzKk7ZcucIOZ0Gr918jX3ObWr91F64hJC3nN 1fUJppekntNIonBq0eCEDOIzNLTw4lwoewnQqUlREO5dgJGoFUlUNJHiWExvBnQrH9 5Fo/LH9LtJ1n2y7hCTUi0oCupcxb7hAcZAmAYw5JPGiqrewJHmHPfD2+BevGErZTIz SKS0/2E0Ij/Ng== Message-ID: Date: Fri, 25 Sep 2026 09:15:06 +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 v6 3/3] mm: implement page refcount locking via dedicated bit To: Zi Yan , Linus Torvalds Cc: Ilya Gladyshev , akpm@linux-foundation.org, andrew+netdev@lunn.ch, apopple@nvidia.com, artem.kuzin@huawei.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, edumazet@google.com, harry.yoo@oracle.com, hramamurthy@google.com, ivgorbunov@me.com, joshwash@google.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, mhocko@suse.com, muchun.song@linux.dev, pfalcato@suse.de, rppt@kernel.org, surenb@google.com, vbabka@suse.cz, willy@infradead.org, yuzhao@google.com References: <56e036665dbeb0a8f51d697220d5ed84f210994c@linux.dev> <570cf649-a8bf-4073-be71-207fbb2bef40@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/25/26 04:44, Zi Yan wrote: > On Thu Sep 24, 2026 at 4:06 PM EDT, Linus Torvalds wrote: >> On Thu, 24 Sept 2026 at 11:52, David Hildenbrand (Arm) wrote: >>> >>> There needs to be a common page freeing function that dipatches stuff. >> >> I think this all needs to be entirely generic to all pages. Agreed. >> Everybody needs to do it right. > > It assumes all callers of page_ref_dec_and_test() are free page > functions, but there are two exceptions: Right, we'll have to sort these out. Which is the right thing to do either way :) > > 1. compaction_free() uses folio_put_testzero(), which calls > page_ref_dec_and_test() to put not used migration dst page back to > isolated freelist instead of freeing them. > > 2. virtio_mem_fake_offline_going_offline() drops the last reference of > fake-offline pages, so that they can be offline. I had a patch for that, where we keep the refcount untouched: https://lore.kernel.org/linux-mm/20250520164216.866543-2-david@redhat.com/ Long-term PG_offline pages will not have a refcount at all, and just have a frozen refcount. That's the right solution long-term: allocate+free them as frozen in virtio-mem. Needs some more work, though :) -- Cheers, David