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Mon, 10 Dec 2018 04:48:54 -0500 Received: from mx2.suse.de ([195.135.220.15]:36646 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726324AbeLJJsy (ORCPT ); Mon, 10 Dec 2018 04:48:54 -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 0ED3EAD6F for ; Mon, 10 Dec 2018 09:48:51 +0000 (UTC) Subject: Re: [PATCH 1/8] btrfs: delayed-ref: Introduce better documented delayed ref structures To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20181206065903.11343-1-wqu@suse.com> <20181206065903.11343-2-wqu@suse.com> From: Nikolay Borisov Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/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/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <235ca34f-bcda-128d-dc3d-7465766271c7@suse.com> Date: Mon, 10 Dec 2018 11:48:50 +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: <20181206065903.11343-2-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 6.12.18 г. 8:58 ч., Qu Wenruo wrote: > Current delayed ref interface has several problems: > - Longer and longer parameter lists > bytenr > num_bytes > parent > ref_root > owner > offset > for_reloc << Only qgroup code cares. > > - Different interpretation for the same parameter > Above @owner for data ref is ino owning this extent, > while for tree ref, it's level. 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 | 109 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 109 insertions(+) > > diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h > index d8fa12d3f2cc..e36d6b05d85e 100644 > --- a/fs/btrfs/delayed-ref.h > +++ b/fs/btrfs/delayed-ref.h > @@ -176,6 +176,81 @@ struct btrfs_delayed_ref_root { > u64 qgroup_to_skip; > }; > > +enum btrfs_ref_type { > + BTRFS_REF_NOT_SET = 0, No need for explicit initialisation when your enums start from 0. > + BTRFS_REF_DATA, > + BTRFS_REF_METADATA, > + BTRFS_REF_LAST, > +}; > + > +struct btrfs_data_ref { > + /* > + * For EXTENT_DATA_REF > + * > + * @ref_root: current owner of the extent. > + * may differ from btrfs_ref::real_root. Here 'owner' is a bit ambiguous. Isn't this the root of the owner > + * @ino: inode number of the owner. And the owner is really the owning inode? > + * @offset: *CALCULATED* offset. Not EXTENT_DATA key offset. What does calculated mean here? > + * > + */ Ugh, this is ugly, why not have a single /* */ line above each member and document them like that? > + u64 ref_root; > + u64 ino; > + u64 offset; > +}; > + > +struct btrfs_tree_ref { > + /* Common for all sub types and skinny combination */ > + int level; Like you've done here. Mention that this is the level in the tree that this reference is located at. > + > + /* > + * For TREE_BLOCK_REF (skinny metadata, either inline or keyed) > + * > + * root here may differ from btrfs_ref::real_root. > + */ Make it refer to the documentation of the generic btrfs_ref structure because if someone reads this comment and doesn't read the one in btrfs_ref then it's not clear under what conditions they might differ. > + u64 root; > + > + /* For non-skinny metadata, no special member needed */ > +}; > + > +struct btrfs_ref { > + enum btrfs_ref_type type; > + int action; > + > + /* > + * Use full backref(SHARED_BLOCK_REF or SHARED_DATA_REF) for this > + * extent and its children. > + * Set for reloc trees. > + */ > + unsigned int use_fullback:1; 'fullback' is too terse, use_backreferences or something conveying more information? Also please use explicit bool type: bool xxxx:1 > + > + /* > + * Whether this extent should go through qgroup record. > + * Normally false, but for certain case like delayed subtree scan, > + * this can hugely reduce qgroup overhead. > + */ > + unsigned int skip_qgroup:1; again, explicit bool type please. > + > + /* > + * Who owns this reference modification, optional. > + * > + * One example: > + * When creating reloc tree for source fs, it will increase tree block > + * ref for children tree blocks. > + * In that case, btrfs_ref::real_root = reloc tree, > + * while btrfs_ref::tree_ref::root = fs tree. > + */ > + u64 real_root; > + u64 bytenr; > + u64 len; > + > + /* Common @parent for SHARED_DATA_REF/SHARED_BLOCK_REF */ OK, it's common but what does it really contain? Either document it or rename it to parent_block or something. > + 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; > @@ -184,6 +259,40 @@ 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 real_root, > + u64 parent) > +{ > + generic_ref->action = action; IMO it makes sense in this series to have a patch which converts the action defines to an enum and subsequently modify functions/structs to actually be of enum type. > + generic_ref->bytenr = bytenr; > + generic_ref->len = len; > + generic_ref->real_root = real_root; > + 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) > { >