From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 81FF0C282CE for ; Mon, 11 Feb 2019 12:55:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 50982218D8 for ; Mon, 11 Feb 2019 12:55:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727431AbfBKMzR (ORCPT ); Mon, 11 Feb 2019 07:55:17 -0500 Received: from mx2.suse.de ([195.135.220.15]:37954 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727106AbfBKMzR (ORCPT ); Mon, 11 Feb 2019 07:55:17 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 19102AC3B for ; Mon, 11 Feb 2019 12:55:15 +0000 (UTC) Subject: Re: [PATCH v3 1/9] btrfs: delayed-ref: Introduce better documented delayed ref structures To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20190211051653.3167-1-wqu@suse.com> <20190211051653.3167-2-wqu@suse.com> From: Nikolay Borisov Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= mQINBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABtCNOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuY29tPokCOAQTAQIAIgUCWIo48QIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQcb6CRuU/KFc0eg/9GLD3wTQz9iZHMFbjiqTCitD7B6dTLV1C ddZVlC8Hm/TophPts1bWZORAmYIihHHI1EIF19+bfIr46pvfTu0yFrJDLOADMDH+Ufzsfy2v HSqqWV/nOSWGXzh8bgg/ncLwrIdEwBQBN9SDS6aqsglagvwFD91UCg/TshLlRxD5BOnuzfzI Leyx2c6YmH7Oa1R4MX9Jo79SaKwdHt2yRN3SochVtxCyafDlZsE/efp21pMiaK1HoCOZTBp5 VzrIP85GATh18pN7YR9CuPxxN0V6IzT7IlhS4Jgj0NXh6vi1DlmKspr+FOevu4RVXqqcNTSS E2rycB2v6cttH21UUdu/0FtMBKh+rv8+yD49FxMYnTi1jwVzr208vDdRU2v7Ij/TxYt/v4O8 V+jNRKy5Fevca/1xroQBICXsNoFLr10X5IjmhAhqIH8Atpz/89ItS3+HWuE4BHB6RRLM0gy8 T7rN6ja+KegOGikp/VTwBlszhvfLhyoyjXI44Tf3oLSFM+8+qG3B7MNBHOt60CQlMkq0fGXd mm4xENl/SSeHsiomdveeq7cNGpHi6i6ntZK33XJLwvyf00PD7tip/GUj0Dic/ZUsoPSTF/mG EpuQiUZs8X2xjK/AS/l3wa4Kz2tlcOKSKpIpna7V1+CMNkNzaCOlbv7QwprAerKYywPCoOSC 7P25Ag0EWIoHPgEQAMiUqvRBZNvPvki34O/dcTodvLSyOmK/MMBDrzN8Cnk302XfnGlW/YAQ csMWISKKSpStc6tmD+2Y0z9WjyRqFr3EGfH1RXSv9Z1vmfPzU42jsdZn667UxrRcVQXUgoKg QYx055Q2FdUeaZSaivoIBD9WtJq/66UPXRRr4H/+Y5FaUZx+gWNGmBT6a0S/GQnHb9g3nonD jmDKGw+YO4P6aEMxyy3k9PstaoiyBXnzQASzdOi39BgWQuZfIQjN0aW+Dm8kOAfT5i/yk59h VV6v3NLHBjHVw9kHli3jwvsizIX9X2W8tb1SefaVxqvqO1132AO8V9CbE1DcVT8fzICvGi42 FoV/k0QOGwq+LmLf0t04Q0csEl+h69ZcqeBSQcIMm/Ir+NorfCr6HjrB6lW7giBkQl6hhomn l1mtDP6MTdbyYzEiBFcwQD4terc7S/8ELRRybWQHQp7sxQM/Lnuhs77MgY/e6c5AVWnMKd/z MKm4ru7A8+8gdHeydrRQSWDaVbfy3Hup0Ia76J9FaolnjB8YLUOJPdhI2vbvNCQ2ipxw3Y3c KhVIpGYqwdvFIiz0Fej7wnJICIrpJs/+XLQHyqcmERn3s/iWwBpeogrx2Lf8AGezqnv9woq7 OSoWlwXDJiUdaqPEB/HmGfqoRRN20jx+OOvuaBMPAPb+aKJyle8zABEBAAGJAh8EGAECAAkF AliKBz4CGwwACgkQcb6CRuU/KFdacg/+M3V3Ti9JYZEiIyVhqs+yHb6NMI1R0kkAmzsGQ1jU zSQUz9AVMR6T7v2fIETTT/f5Oout0+Hi9cY8uLpk8CWno9V9eR/B7Ifs2pAA8lh2nW43FFwp IDiSuDbH6oTLmiGCB206IvSuaQCp1fed8U6yuqGFcnf0ZpJm/sILG2ECdFK9RYnMIaeqlNQm iZicBY2lmlYFBEaMXHoy+K7nbOuizPWdUKoKHq+tmZ3iA+qL5s6Qlm4trH28/fPpFuOmgP8P K+7LpYLNSl1oQUr+WlqilPAuLcCo5Vdl7M7VFLMq4xxY/dY99aZx0ZJQYFx0w/6UkbDdFLzN upT7NIN68lZRucImffiWyN7CjH23X3Tni8bS9ubo7OON68NbPz1YIaYaHmnVQCjDyDXkQoKC R82Vf9mf5slj0Vlpf+/Wpsv/TH8X32ajva37oEQTkWNMsDxyw3aPSps6MaMafcN7k60y2Wk/ TCiLsRHFfMHFY6/lq/c0ZdOsGjgpIK0G0z6et9YU6MaPuKwNY4kBdjPNBwHreucrQVUdqRRm RcxmGC6ohvpqVGfhT48ZPZKZEWM+tZky0mO7bhZYxMXyVjBn4EoNTsXy1et9Y1dU3HVJ8fod 5UqrNrzIQFbdeM0/JqSLrtlTcXKJ7cYFa9ZM2AP7UIN9n1UWxq+OPY9YMOewVfYtL8M= Message-ID: <216f4acf-faf9-6ca3-c9f2-68a9eaa763fa@suse.com> Date: Mon, 11 Feb 2019 14:55:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20190211051653.3167-2-wqu@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 11.02.19 г. 7:16 ч., Qu Wenruo wrote: > Current delayed ref interface has several problems: > - Longer and longer parameter lists > bytenr > num_bytes > parent > ---------- so far so good > ref_root > owner > offset > ---------- I don't feel good now > > - Different interpretation for the same parameter > Above @owner for data ref is inode number (u64), > while for tree ref, it's level (int). > > They are even in different size range. > For level we only need 0~8, while for ino it's > BTRFS_FIRST_FREE_OBJECTID~BTRFS_LAST_FREE_OBJECTID. > > And @offset doesn't even makes sense for tree ref. > > Such parameter reuse may look clever as an hidden union, but it > destroys code readability. > > To solve both problems, we introduce a new structure, btrfs_ref to solve > them: > > - Structure instead of long parameter list > This makes later expansion easier, and better documented. > > - Use btrfs_ref::type to distinguish data and tree ref > > - Use proper union to store data/tree ref specific structures. > > - Use separate functions to fill data/tree ref data, with a common generic > function to fill common bytenr/num_bytes members. > > All parameters will find its place in btrfs_ref, and an extra member, > @real_root, inspired by ref-verify code, is newly introduced for later > qgroup code, to record which tree is triggered this extent modification. > > This patch doesn't touch any code, but provides the basis for incoming > refactors. > > Signed-off-by: Qu Wenruo > --- > fs/btrfs/delayed-ref.h | 116 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 116 insertions(+) > > diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h > index d2af974f68a1..24addc5163bc 100644 > --- a/fs/btrfs/delayed-ref.h > +++ b/fs/btrfs/delayed-ref.h > @@ -187,6 +187,90 @@ struct btrfs_delayed_ref_root { > u64 qgroup_to_skip; > }; > > +enum btrfs_ref_type { > + BTRFS_REF_NOT_SET, > + BTRFS_REF_DATA, > + BTRFS_REF_METADATA, > + BTRFS_REF_LAST, > +}; > + > +struct btrfs_data_ref { > + /* For EXTENT_DATA_REF */ > + > + /* Root who refers to this data extent */ nit: s/who/which/ > + u64 ref_root; > + > + /* Inode who refers to this data extent */ nit: DITTO > + u64 ino; > + > + /* > + * file_offset - extent_offset > + * > + * file_offset is the key.offset of the EXTENT_DATA key. > + * extent_offset is btrfs_file_extent_offset() of the EXTENT_DATA data. > + */ This needs rewording since it's rather cryptic now. Looking at the dev docs and the description for 'offset' field in btrfs_file_extent_item I can sort of deduce that this field will only be different than null if this reference is for an extent which is shared between 2 snapshots. So if file foo is shared between two snapshots, has 1 extent and in snapshot2 this extent is partially changed then I'd expect extent_offset to point to the start in the original (unchanged extent), correct? > + u64 offset; > +}; > + > +struct btrfs_tree_ref { > + /* > + * Level of this tree block > + * > + * Shared for skinny (TREE_BLOCK_REF) and normal tree ref. This sentence is also not very clear? You mean this level applies to tree block refs (irrespective of whether they are shared or normal tree block refs)? > + */ > + int level; > + > + /* > + * Root who refers to this tree block. nit:s/who/which > + * > + * For TREE_BLOCK_REF (skinny metadata, either inline or keyed) > + */ > + u64 root; > + > + /* For non-skinny metadata, no special member needed */ > +}; > + > +struct btrfs_ref { > + enum btrfs_ref_type type; > + int action; > + > + /* > + * Only use parent pointers as backref (SHARED_BLOCK_REF or > + * SHARED_DATA_REF) for this extent and its children. > + * Set for reloc trees. > + */ > + bool only_backreferences:1; > + > + /* > + * Whether this extent should go through qgroup record. > + * > + * Normally false, but for certain case like delayed subtree scan, > + * setting this flag can hugely reduce qgroup overhead. > + */ > + bool skip_qgroup:1; > + > + /* > + * Optional. To which root this modification is for. > + * Mostly used for qgroup optimization. > + * > + * When unset, data/tree ref init code will populate it. > + * In certain case, we're modifying reference for a different root. > + * E.g. Cow fs tree blocks for balance. > + * In that case, tree_ref::root will be fs tree, but we're doing this > + * for reloc tree, then we should set @real_root to reloc tree. > + */ > + u64 real_root; > + u64 bytenr; > + u64 len; > + > + /* Bytenr of the parent tree block */ > + u64 parent; > + union { > + struct btrfs_data_ref data_ref; > + struct btrfs_tree_ref tree_ref; > + }; > +}; > + > extern struct kmem_cache *btrfs_delayed_ref_head_cachep; > extern struct kmem_cache *btrfs_delayed_tree_ref_cachep; > extern struct kmem_cache *btrfs_delayed_data_ref_cachep; > @@ -195,6 +279,38 @@ extern struct kmem_cache *btrfs_delayed_extent_op_cachep; > int __init btrfs_delayed_ref_init(void); > void __cold btrfs_delayed_ref_exit(void); > > +static inline void btrfs_init_generic_ref(struct btrfs_ref *generic_ref, > + int action, u64 bytenr, u64 len, u64 parent) > +{ > + generic_ref->action = action; > + generic_ref->bytenr = bytenr; > + generic_ref->len = len; > + generic_ref->parent = parent; > +} > + > +static inline void btrfs_init_tree_ref(struct btrfs_ref *generic_ref, > + int level, u64 root) > +{ > + /* If @real_root not set, use @root as fallback */ > + if (!generic_ref->real_root) > + generic_ref->real_root = root; > + generic_ref->tree_ref.level = level; > + generic_ref->tree_ref.root = root; > + generic_ref->type = BTRFS_REF_METADATA; > +} > + > +static inline void btrfs_init_data_ref(struct btrfs_ref *generic_ref, > + u64 ref_root, u64 ino, u64 offset) > +{ > + /* If @real_root not set, use @root as fallback */ > + if (!generic_ref->real_root) > + generic_ref->real_root = ref_root; > + generic_ref->data_ref.ref_root = ref_root; > + generic_ref->data_ref.ino = ino; > + generic_ref->data_ref.offset = offset; > + generic_ref->type = BTRFS_REF_DATA; > +} > + > static inline struct btrfs_delayed_extent_op * > btrfs_alloc_delayed_extent_op(void) > { >