From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A7BFD6E619; Wed, 4 Sep 2024 17:39:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725471582; cv=none; b=lCk0xutvj5jeAzv9iUSERApyjm2rZbU+MDq7XJ6xTni/nRI7EORIkYac1Gt0NQc3cB7KhUiEV/UIsuh+iisuMTaywrh70WuQnJBng26hbJ+hWsyCD9vPYlZYaFA6V3H0P5lkJe4e1WvP+M3AnvmmTy6dzNs0+tJ44y0mpoa3GU4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725471582; c=relaxed/simple; bh=ydYZY7v7ruTG2d3pFr0sYhTXJYpdllJL3bZ7mdEGhtc=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=TXeEJ5AY8CpqOAMLFxJcicaiF0tp5u0j6fdOr+POj45DEbSOzExjMgJdFGIX0zgGZtV6/OHQl1B3L4CUh1syW4ZH3gjDXsZapdGQ6/2rLg6kSEZ9NPVpm2BwQhINVJtXASBU23Ym0rehnU7LRqzORVa1bUOro8qocAjUaXAmPAQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SkoYEsP/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SkoYEsP/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B4560C4CEC2; Wed, 4 Sep 2024 17:39:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725471582; bh=ydYZY7v7ruTG2d3pFr0sYhTXJYpdllJL3bZ7mdEGhtc=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=SkoYEsP/ap8vBwx+/K1MQOJcE2X78/ExYLoEAvAegdn6PMDtsocZl8obKE5x/Tg9r /sJXUNyUhfFAZ0t89zKv+b0vY4Jua8EBYXGo7VnqJySkH/MQ1I0SAJIGd+/ZXZhJN6 T0Z5JTy6u9l1YwfRwzg8RGsDYY6fMg/2G/fwj4IVlmr9tWqG1WyjsbiN6n5Fni0ww7 rR52L1f+sSpDA0CWnLthCio7KtqX8p9eLXer74ZKDigFNimFR/rknMRukTxGRJnGDv CG8Tda51OrgfwE7W8I8fWQPkXPgn393GntAzmv6OpTT1KVY1B1IOB4IJSgua0stxOm 7PIEjCRytrvdw== Message-ID: <2ae8b2d1e2f22fba5acb88c3f12cef9716f28a62.camel@kernel.org> Subject: Re: [PATCH v3 03/13] nfsd: drop the ncf_cb_bmap field From: Jeff Layton To: Chuck Lever III Cc: Neil Brown , Olga Kornievskaia , Dai Ngo , Tom Talpey , Trond Myklebust , Anna Schumaker , Olga Kornievskaia , Al Viro , Christian Brauner , Jan Kara , Jonathan Corbet , Tom Haynes , Linux Kernel Mailing List , Linux NFS Mailing List , Linux FS Devel , "linux-doc@vger.kernel.org" Date: Wed, 04 Sep 2024 13:39:39 -0400 In-Reply-To: <52C563DF-88D1-4AAC-B441-9B821A7B32FF@oracle.com> References: <20240829-delstid-v3-0-271c60806c5d@kernel.org> <20240829-delstid-v3-3-271c60806c5d@kernel.org> <82b17019fb334973a74adf88e3eb255df4091f12.camel@kernel.org> <52C563DF-88D1-4AAC-B441-9B821A7B32FF@oracle.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; 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text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.4 (3.52.4-1.fc40) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2024-09-04 at 17:28 +0000, Chuck Lever III wrote: >=20 > > On Sep 4, 2024, at 12:58=E2=80=AFPM, Jeff Layton w= rote: > >=20 > > On Wed, 2024-09-04 at 11:20 -0400, Chuck Lever wrote: > > > On Thu, Aug 29, 2024 at 09:26:41AM -0400, Jeff Layton wrote: > > > > This is always the same value, and in a later patch we're going to = need > > > > to set bits in WORD2. We can simplify this code and save a little s= pace > > > > in the delegation too. Just hardcode the bitmap in the callback enc= ode > > > > function. > > > >=20 > > > > Signed-off-by: Jeff Layton > > >=20 > > > OK, lurching forward on this ;-) > > >=20 > > > - The first patch in v3 was applied to v6.11-rc. > > > - The second patch is now in nfsd-next. > > > - I've squashed the sixth and eighth patches into nfsd-next. > > >=20 > > > I'm replying to this patch because this one seems like a step > > > backwards to me: the bitmap values are implementation-dependent, > > > and this code will eventually be automatically generated based only > > > on the protocol, not the local implementation. IMO, architecturally, > > > bitmap values should be set at the proc layer, not in the encoders. > > >=20 > > > I've gone back and forth on whether to just go with it for now, but > > > I thought I'd mention it here to see if this change is truly > > > necessary for what follows. If it can't be replaced, I will suck it > > > up and fix it up later when this encoder is converted to an xdrgen- > > > manufactured one. > >=20 > > It's not truly necessary, but I don't see why it's important that we > > keep a record of the full-blown bitmap here. The ncf_cb_bmap field is a > > field in the delegation record, and it has to be carried around in > > perpetuity. This value is always set by the server and there are only a > > few legit bit combinations that can be set in it. > >=20 > > We certainly can keep this bitmap around, but as I said in the > > description, the delstid draft grows this bitmap to 3 words, and if we > > want to be a purists about storing a bitmap, >=20 > Fwiw, it isn't purism about storing the bitmap, it's > purism about adopting machine-generated XDR marshaling/ > unmarshaling code. The patch adds non-marshaling logic > in the encoder. Either we'll have to add a way to handle > that in xdrgen eventually, or we'll have to exclude this > encoder from machine generation. (This is a ways down the > road, of course) > Understood. I'll note that this function works with a nfs4_delegation pointer too, which is not part of the protocol spec. Once we move to autogenerated code, we will always have a hand-rolled "glue" layer that morphs our internal representation of these sorts of objects into a form that the xdrgen code requires. Storing this info as a flag in the delegation makes more sense to me, as the glue layer should massage that into the needed form. >=20 > > then that will also > > require us to keep the bitmap size (in another 32-bit word), since we > > don't always want to set anything in the third word. That's already 24 > > extra bits per delegation, and we'll be adding new fields for the > > timestamps in a later patch. > >=20 > > I don't see the benefit here. >=20 > Understood, there's a memory scalability issue. >=20 > There are other ways to go about this that do not grow > the size of the delegation data structure, I think. For > instance, you could store the handful of actual valid > bitmap values in read-only memory, and have the proc > function select and reference one of them. IIRC the > client already does this for certain GETATTR operations. >=20 Unfortunately, it turns out that the bitmap is a bit more complicated, and we don't quite do it right today. I did a more careful read of section 10.4.3 in RFC8881. It has this pseudocode: if (!modified) { do CB_GETATTR for change and size; if (cc !=3D sc) modified =3D TRUE; } else { do CB_GETATTR for size; } if (modified) { sc =3D sc + 1; time_modify =3D time_metadata =3D current_time; update sc, time_modify, time_metadata into file's metadata; } Note that if the thing is already considered to be modified, then it says to not request FATTR4_CHANGE. I have a related question around this on the IETF list too. > So, leave this patch as is, and I will deal with it > later when we convert the callback XDR functions. >=20 Thanks, will do. --=20 Jeff Layton