Return-Path: Received: from mail-ua0-f174.google.com ([209.85.217.174]:33359 "EHLO mail-ua0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751438AbdBUVVG (ORCPT ); Tue, 21 Feb 2017 16:21:06 -0500 Received: by mail-ua0-f174.google.com with SMTP id h65so13724703uah.0 for ; Tue, 21 Feb 2017 13:21:06 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: <1487470070-32358-1-git-send-email-bfields@redhat.com> <1487470070-32358-7-git-send-email-bfields@redhat.com> <1D136924-2EC7-4CF3-8250-98799DFBEB3F@oracle.com> <20170220160940.GB12335@parsley.fieldses.org> <4824B968-4ED6-44AA-A935-3D309D76EFFF@oracle.com> <20170220171519.GE12335@parsley.fieldses.org> From: Andreas Gruenbacher Date: Tue, 21 Feb 2017 22:21:05 +0100 Message-ID: Subject: Re: [PATCH 6/6] NFSv4: allow getacl rpc to allocate pages on demand To: Chuck Lever Cc: "J. Bruce Fields" , Trond Myklebust , Anna Schumaker , Linux NFS Mailing List , Dros Adamson , Weston Andros Adamson Content-Type: text/plain; charset=UTF-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Tue, Feb 21, 2017 at 7:46 PM, Chuck Lever wrote: > Hi Andreas- > > >> On Feb 20, 2017, at 4:31 PM, Andreas Gruenbacher wrote: >> >> On Mon, Feb 20, 2017 at 6:15 PM, J. Bruce Fields wrote: >>> On Mon, Feb 20, 2017 at 11:42:31AM -0500, Chuck Lever wrote: >>>> >>>>> On Feb 20, 2017, at 11:09 AM, J. Bruce Fields wrote: >>>>> >>>>> On Sun, Feb 19, 2017 at 02:29:03PM -0500, Chuck Lever wrote: >>>>>> >>>>>>> On Feb 18, 2017, at 9:07 PM, J. Bruce Fields wrote: >>>>>>> >>>>>>> From: Weston Andros Adamson >>>>>>> >>>>>>> Instead of preallocating pags, allow xdr_partial_copy_from_skb() to >>>>>>> allocate whatever pages we need on demand. This is what the NFSv3 ACL >>>>>>> code does. >>>>>> >>>>>> The patch description does not explain why this change is >>>>>> being done. >>>>> >>>>> The only justification I see is avoiding allocating pages unnecessarily. >>>> >>>> That makes sense. Is there a real world workload that has seen >>>> a negative effect? >>>> >>>> >>>>> Without this patch, for each getacl, we allocate 17 pages (if I'm >>>>> calculating correctly) and probably rarely use most of them. >>>>> >>>>> In the v3 case I think it's 7 pages instead of 17. >>>> >>>> I would have guessed 9. Out of curiosity, is there a reason >>>> documented for these size limits? >>> >>> >>> In the v4 case: >>> >>> #define NFS4ACL_MAXPAGES DIV_ROUND_UP(XATTR_SIZE_MAX, PAGE_SIZE) >>> >>> And I believe XATTR_SIZE_MAX is a global maximum on the size of any >>> extend attribute value. >> >> XATTR_SIZE_MAX is the maximum size of an extended attribute. NFSv4 >> ACLs are passed through unchanged in "system.nfs4_acl". > > "Extended attribute" means this is a Linux-specific limit? Yes. > Is there anything that prevents a non-Linux system from constructing > or returning an ACL that is larger than that? No. > What happens on a Linux client when a server returns an ACL that does > not fit in this allotment? I would hope an error, but I haven't tested it. Andreas