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 3A01114A60F; Sat, 10 Oct 2026 03:18:59 +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=1791602341; cv=none; b=Z9U1WBnRhtIA3ON12Itv9Fj+XVbCarDrlKMuQ4pWLaJ3jLrl0brkEv9VkTGvDsEnBJNtEa1SoTt4hlLywyVUkCGabORUH+1B7iw39HgxLwrFHFruPPvuYBfgN/mibSS2FhUjYQf9MP2uwFm8M7uvgjyWS5QNlYyyWrQ+sO1NvFo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791602341; c=relaxed/simple; bh=QhscVVAhAWdzZMvxnfWngyElPv80yj6D4SS6D1Dq7yQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=r3wInzgAs0HwweI8jJ5yX0QFymdAvWYfVgjD+3lgjl3EOlQsbzxQlREU5Gj/bZcoQCsmU38eBnjuMQlVi92OkDbQP9JhdfTPuPWH7BvYnx/OTJfzEebEtVDl9l+qsjYYe4a4jJyunIEATMgYGvhMFQaaykW1iHjnkJa/RZX7O9U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jVmjNQFt; 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="jVmjNQFt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B42761F000FF; Sat, 10 Oct 2026 03:18:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791602339; bh=mvErx1WWrmavZpAWawNx/SxSWFSIPpRG5LFKnvSw2A0=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=jVmjNQFtVai+W7WXC+h3kBaL0yjWXjUQJYTf2QnXM6D3GAH9/NAhARUSIpFOV0ocz ldAQ277Wo7iqm+PAjlF23ZdAK1uixhqlEROEG4z6b13Dftr/BL+rzd6RoAuKK5qweZ CUe5/3NsUdVjpRG/ava7nnO58ZC5r8ewUiFIB+xTaOUcmHx1krhNwlHvU6+KWDQplT RA1laodn+A61NsVE/vx1EED1Ew5/AINNnK9pSkEWxhOllREjl9+3cxE6oRP+GKBfdc Jj9BT6Foz6Is5IHwk76OmFoK50H788A3TiXNzSJGWK9kt+ceeBVH3TG0EOeu4FAfwo j8pwAY4y1zMdw== Date: Fri, 9 Oct 2026 20:18:59 -0700 From: Kees Cook To: Harry Yoo Cc: Vlastimil Babka , Christian Brauner , Jan Kara , Andrew Morton , Roman Gushchin , Johannes Weiner , Michal Hocko , Shakeel Butt , Muchun Song , cgroups@vger.kernel.org, linux-mm@kvack.org, Pedro Falcato , Kuniyuki Iwashima , linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v6 2/8] ipc, msg: Account msg_msg allocations with GFP_KERNEL_ACCOUNT again Message-ID: <202610092014.AAB20B81@keescook> References: <20261006092030.got.500-kees@kernel.org> <20261006092035.166776-2-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@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: On Fri, Oct 09, 2026 at 09:39:48PM +0200, Harry Yoo wrote: > On Fri, Oct 09, 2026 at 04:22:03PM +0200, Harry Yoo wrote: > > And now I see the initial kmem_buckets design did not sufficiently > > tackle the question "How this should work when kmem_buckets falls back > > to kmalloc?" > > > > I suppose the kmem_buckets' abstraction should not be too tightly > > coupled with kmalloc caches. Creating a kmem_buckets should be > > conceptually equivalent to creating a set of caches with speicifc > > slab flags, size, align, useroffset/size. (for variable size allocation). > > Just to clarify... I have a few concerns on this area. > > 1. Complexity. > > It's very counter-intuitive to understand how it works when > SLAB_BUCKETS is not compiled. My brain cannot easily process two > different implementations w/ and w/o SLAB_BUCKETS. > > A "compatibility layer" allows us to assume certain expectations > and ignore all implementation details when SLAB_BUCKETS is not compiled. I'd rather make kmem_buckets not have a SLAB_BUCKETS option. :) > 2. Making kmem_buckets tightly coupled with kmalloc's implementation > details is not reasonable. > > Let's say, at some point we make SLAB_BUCKETS always enabled and drop > the config option. Then all kmem_buckets users will now have certain > assumptions inherted from kmalloc (e.g. alignment), which is not > reasonable. Until it's always enabled, I don't see a reasonable way to separate those assumptions. > 3. __GFP_ACCOUNT and __GFP_DMA should be applied to all allocations > in the slab cache. For kmalloc, these flags are only used to select > the kmalloc cache (which has equivalent SLAB_* flags for __GFP_ACCOUNT > or __GFP_DMA) to serve the allocation. > > Specifying it on individual allocations (rather than as SLAB_ flags) > makes it easy to break the assumption. As in, you don't want a "pass-through" mode for __GFP_DMA? It's a lot of overhead for __GFP_DMA to have multiple providers, so I'd rather allow kmem_buckets to allow pass-through (perhaps explicitly opt-in) where then the other options (e.g. alignment) must match the general kmalloc caches so that pass-through is consistent. > > When it falls back to kmalloc, kmem_buckets itself should provide a > > compatibility layer when falling back to kmalloc. > > For example, calculate_sizes() converts certain SLAB_* flags into > GFP flags (s->allocflags) for allocation. We can have a similar > logic when falling back to kmalloc. > > Though current implementation does not allow this and requires > some rework. I think the current series does everything correctly in the sense that nothing is allowing for mismatched fallbacks/passthrus. We could iterate from there once we have a need for this where a non-kmalloc-alignment is wanted, etc? -- Kees Cook