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 836482D8385 for ; Tue, 2 Jun 2026 12:52:05 +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=1780404726; cv=none; b=p8cJbaesvE9x1YzvfD+vWbVipfiFfA9wWw3xQmJC6M4wVHKaQcbtqbYcvh7A7PR93gsNQ0e+aIvnWuTBvIvFP/cLU2nW4rR4RB+gkwuzvWa/uiWv9TWZRTr7Yy9aZaPcqHKRY59ZfgHLWWaeCM1iGlFQcUYWiFrK44MKss0MvHc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780404726; c=relaxed/simple; bh=Ih8H8CgMVuC0Dww3vrp3jULDOqoIb9te2p94WfrVoX0=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=iG4meuEMY2XX2tAEpPpzKdsoycqUqY2xg9S8aYxgdOcIlCRqwK2tk17kutxXLw4+QfPC+jhN1iB989hvbXVX7K3rQSayQ+d6Tz9bdgDQvi/9tmN2+zuPVlCUOVL9owqiCQzF1CWXm+OEGTgac9j2VkzeyWIcBvZ7/VdWnUFD1N4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IiXf1nVA; 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="IiXf1nVA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F8561F00893; Tue, 2 Jun 2026 12:52:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1780404725; bh=QoEDHLDPjah5bpcTq5+xdPnUnkR+I3T5o+EEfuYH6c0=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=IiXf1nVAnO6t8NjlmzVhB2FDUs+qCYUsODkAWZ8sJTmk6a3lKVlf7tG67+VzbgBNQ J7k5dqFFIF6+G5gn8Eq+IwMN4aNjsd2ONhT4EHoruasOEleK7cSmsQB4YdlAAqGEz5 4FFIzpTYiIeOCxlkgCfydz5dzQERCV/6b4kvoHr8KvCEruq64LWvoxFZdT6q5i006q iwkVYLG0Ss7xNCtzrvg/VjiGJkSmKi+s2M36PLANDh6Y4h0ZjEEtyAlvpn63SbHQ0l Jjk5kCalZ1XzlknpjzXB5XVn3uybFmWbzn4yCt1wGKZNiOh2bkPsibCvLd99WXllys 7B1hR1+e6qUMQ== From: Pratyush Yadav To: Mike Rapoport Cc: Pratyush Yadav , Pasha Tatashin , Alexander Graf , Muchun Song , Oscar Salvador , David Hildenbrand , Andrew Morton , Jason Miu , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 09/12] memblock: introduce MEMBLOCK_KHO_SCRATCH_EXT In-Reply-To: (Mike Rapoport's message of "Sun, 31 May 2026 21:51:09 +0300") References: <20260429133928.850721-1-pratyush@kernel.org> <20260429133928.850721-10-pratyush@kernel.org> <2vxzecjhc2s8.fsf@kernel.org> <2vxzse7j7ai9.fsf@kernel.org> Date: Tue, 02 Jun 2026 14:52:02 +0200 Message-ID: <2vxztsrlds0d.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Sun, May 31 2026, Mike Rapoport wrote: > On Fri, May 22, 2026 at 05:02:38PM +0200, Pratyush Yadav wrote: >> On Fri, May 22 2026, Pasha Tatashin wrote: >> >> > On 05-11 18:46, Pratyush Yadav wrote: >> >> On Mon, May 11 2026, Mike Rapoport wrote: >> >> >> >> > On Wed, Apr 29, 2026 at 03:39:11PM +0200, Pratyush Yadav wrote: >> >> >> From: "Pratyush Yadav (Google)" >> >> >> >> >> >> In the upcoming commits, the KHO will learn how to discover free blocks >> >> >> of memory by walking the KHO radix tree. It will then mark those regions >> >> >> as scratch to allow memory allocation in case scratch runs low. >> >> >> >> >> >> To differentiate the extended scratch areas from the main scratch areas, >> >> >> introduce MEMBLOCK_KHO_SCRATCH_EXT. Use it when choosing memblock flags >> >> >> for allocations during scratch-only. Teach should_skip_region() to check >> >> >> for both flags before deciding if the region should be skipped. >> >> > >> >> > Why there's a need to differentiate SCRATCH and SCRATCH_EXT? >> >> > SCRATCH (I still hate the name) means "memory memblock can safely use for >> > >> > +1000 >> > >> > I also strongly dislike this name and mentioned it in another thread >> > earlier today. >> > >> > If we ever decide to s/scratch/something-else/ globally, that should be a >> > separate cleanup effort. However, since we are introducing a brand new flag >> > here, we can discuss a better name for the _ext portion to avoid overloading >> > the "scratch" concept. >> > >> >> > the allocations". Initially this memory comes from the reservations in the >> >> > first kernel, but if the second kernel can find more memory to extend it, >> >> > why that additional memory should be treated differently? >> >> >> >> Two reasons: >> >> >> >> 1. We mark SCRATCH as MIGRATE_CMA. We don't want to do that for >> >> SCRATCH_EXT since this memory can be used for non-movable >> >> allocations. >> >> >> >> 2. Gigantic (1G) huge pages can not be allocated from scratch. They can >> >> be preserved memory and thus should not be allocated from SCRATCH. >> >> See patch 12 that does allocations for gigantic huge pages only from >> >> SCRATCH_EXT. >> >> >> >> I will add this in the commit message for the next version. >> >> >> >> Naming is hard, so if you have any better names I'm all ears :-) >> > >> > IMO, this scratch_ext is not "scratch" in the traditional KHO sense at all. >> > The traditional KHO scratch is what is passed from kernel to kernel and is >> > guaranteed to contain zero preserved memory. This new memory is not passed >> > from kernel to kernel and can contain preserved memory at runtime. It's >> > essentially just memory that we identify as currently unpreserved and release >> > early to the system. >> > >> > If we want to keep the naming aligned with the existing codebase for now: >> > MEMBLOCK_KHO_SCRATCH -> original scratch >> > MEMBLOCK_KHO_UNPRESERVED -> for the new memory (instead of SCRATCH_EXT) >> >> UNPRESERVED sounds good to me. I will use that for the next revision >> unless Mike objects. > > Can we make it shorter? ;-) > > UNPRESERVED makes sense, although I'd love to completely remove KHO_ notion > and make the name reflect how it's used by memblock. I was toying with > PREFERRED instead of SCRATCH, but it didn't feel right enough. > With two of them that surely won't work :) I don't think you really can remove KHO_ notion. These memory regions only make sense on a KHO boot, and won't exist otherwise. And PREFERRED sounds like a suggestion/priority hint, not a hard limit. "With KHO boot, you can _only_ use PREFERRED memory", doesn't sound right... I think MEMBLOCK_KHO_BOOTMEM for scratch and MEMBLOCK_KHO_NOPRESERVE (which I think is a tiny bit better than UNPRESERVED) for scratch_ext are my top picks. To make it shorter, perhaps MEMBLOCK_KHO_NOPRSRV, in similar fashion to RSRV_KERN? > >> > Alternatively, if we do want to tackle the global rename of "scratch" later: >> > MEMBLOCK_KHO_BOOTSTRAP -> for the original scratch >> > MEMBLOCK_KHO_UNPRESERVED -> for this new dynamic memory >> >> Or perhaps BOOTMEM? I suppose either of the two are somewhat better than >> scratch. > > Well, if we have BOOTMEM_HVO, we can have BOOTMEM_KHO as well :) > >> Anyway, can we please do the SCRATCH rename as a separate series? I > > Sure. We can continue bikeshedding in parallel. > >> would like this series to not get muddled in the naming discussion. I >> will use UNPRESERVED for the new concept in v2 though. > > That might warrant v3 even if everything else is perfect :) I can live with that. As long as we can agree on the easy part (the code), I don't mind doing another version for the hard part (the naming) ;-) -- Regards, Pratyush Yadav