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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Alexander Viro , Christoph Hellwig , Jens Axboe , Jeffrey Layton , Christian Brauner , Linus Torvalds , "netdev@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Anna Schumaker , Charles Edward Lever , "linux-nfs@vger.kernel.org" Subject: Re: [RFC PATCH 27/28] sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage Thread-Topic: [RFC PATCH 27/28] sunrpc: Use sendmsg(MSG_SPLICE_PAGES) rather then sendpage Thread-Index: AQHZWBvarYtr7Kf76ku/+p4ZPGQrUa79lXMAgAAB/4CAABBbgA== Date: Thu, 16 Mar 2023 17:23:26 +0000 Message-ID: <8F8B62FD-0F16-4383-BB34-97E850DAA7AF@hammerspace.com> References: <3DFBF27C-A62B-4AFE-87FD-3DF53FC39E8E@hammerspace.com> <20230316152618.711970-1-dhowells@redhat.com> <20230316152618.711970-28-dhowells@redhat.com> <754534.1678983891@warthog.procyon.org.uk> In-Reply-To: <754534.1678983891@warthog.procyon.org.uk> Accept-Language: en-US, en-GB Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3731.400.51.1.1) x-ms-publictraffictype: Email x-ms-traffictypediagnostic: CH0PR13MB5084:EE_|PH0PR13MB5715:EE_ x-ms-office365-filtering-correlation-id: a94a5dc1-9635-4618-4c8c-08db26432722 x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable On Mar 16, 2023, at 12:24, David Howells wrote: Trond Myklebust wrote: + buf->bvec +=3D 2; + buf->bvec[-2].bv_page =3D NULL; + buf->bvec[-1].bv_page =3D NULL; NACK. Can you elaborate? Is it that you dislike allocating extra slots for protocol bits? Or just t= hat the bvec[] is offset by 2? Or some other reason? 1) This is code that is common to the client and the server. Why are we add= ing unused 3 bvec slots to every client RPC call? 2) It obfuscates the existence of these bvec slots. 3) knfsd may use splice_direct_to_actor() in order to avoid copying the pag= e cache data into private buffers (it just takes a reference to the pages).= Using MSG_SPLICE_PAGES will presumably require it to protect those pages a= gainst further writes while the socket is referencing them. _________________________________ Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@hammerspace.com --_000_8F8B62FD0F164383BB3497E850DAA7AFhammerspacecom_ Content-Type: text/html; charset="us-ascii" Content-ID: <2FD585A87828A748A045B4171FC0E0E5@namprd13.prod.outlook.com> Content-Transfer-Encoding: quoted-printable

On Mar 16, 2023, at 12:24, David Howells <dhowells@redhat.com> w= rote:

Trond Myklebust <trondmy@hammerspace.com> wrote:

+ buf->bvec +=3D 2;
+ buf->bvec[-2].bv_page =3D NULL;
+ buf->bvec[-1].bv_page =3D NULL;

NACK.

Can you elaborate?

Is it that you dislike allocating extra slots for protocol bits?  Or j= ust that
the bvec[] is offset by 2?  Or some other reason?


1) This is code that is common to the client and the server. Why are w= e adding unused 3  bvec slots to every client RPC call?
2) It obfuscates the existence of these bvec slots.
3) knfsd may use splice_direct_to_actor() in order to avoid copying th= e page cache data into private buffers (it just takes a reference to the pa= ges). Using MSG_SPLICE_PAGES will presumably require it to protect those pa= ges against further writes while the socket is referencing them.


_________________________________
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com

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