From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chao Yu Subject: Re: [PATCH 2/2] f2fs: support {d,id,did,x}node checksum Date: Tue, 27 Feb 2018 22:16:58 +0800 Message-ID: <3782ed9e-741d-d711-3937-bc8127566982@kernel.org> References: <20180127094301.29154-1-yuchao0@huawei.com> <20180127094301.29154-2-yuchao0@huawei.com> <20180131020213.GA86468@jaegeuk-macbookpro.roam.corp.google.com> <20180131221531.GC12901@jaegeuk-macbookpro.roam.corp.google.com> <55f144df-4419-3642-5b35-c8885cdb7354@kernel.org> <20180210014140.GB1885@jaegeuk-macbookpro.roam.corp.google.com> <5f22d645-001d-a132-f0bd-2dba1f6daaea@kernel.org> <558ea6b1-e57d-5910-d931-a47f143cca25@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <558ea6b1-e57d-5910-d931-a47f143cca25@huawei.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Chao Yu , Jaegeuk Kim Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org List-Id: linux-f2fs-devel.lists.sourceforge.net Ping, On 2018/2/13 15:34, Chao Yu wrote: > Hi Jaegeuk, > > On 2018/2/10 10:52, Chao Yu wrote: >> On 2018/2/10 9:41, Jaegeuk Kim wrote: >>> On 02/01, Chao Yu wrote: >>>> >>>> >>>> On 2018/2/1 6:15, Jaegeuk Kim wrote: >>>>> On 01/31, Chao Yu wrote: >>>>>> On 2018/1/31 10:02, Jaegeuk Kim wrote: >>>>>>> What if we want to add more entries in addition to node_checksum? Do we have >>>>>>> to add a new feature flag at every time? How about adding a layout value instead >>>>>> >>>>>> Hmm.. for previous implementation, IMO, we'd better add a new feature flag at >>>>>> every time, otherwise, w/ extra_nsize only, in current image, we can know a >>>>>> valid range of extended area in node block, but we don't know which >>>>>> fields/features are valid/enabled or not. >>>>>> >>>>>> One more thing is that if we can add one feature flag for each field, we got one >>>>>> more chance to disable it dynamically. >>>>>> >>>>>>> of extra_nsize? For example, layout #1 means node_checksum with extra_nsize=X? >>>>>>> >>>>>>> >>>>>>> What does 1017 mean? We need to make this structure more flexibly for new >>>>>> >>>>>> Yes, using raw 1017 is not appropriate here. >>>>>> >>>>>>> entries. Like this? >>>>>>> union { >>>>>>> struct node_v1; >>>>>>> struct node_v2; >>>>>>> struct node_v3; >>>>>>> ... >>>>>>> struct direct_node dn; >>>>>>> struct indirect_node in; >>>>>>> }; >>>>>>> }; >>>>>>> >>>>>>> struct node_v1 { >>>>>>> __le32 data[DEF_ADDRS_PER_BLOCK - V1_NSIZE=1]; >>>>>>> __le32 node_checksum; >>>>>>> } >>>>>>> >>>>>>> struct node_v2 { >>>>>>> __le32 data[DEF_ADDRS_PER_BLOCK - V2_NSIZE=500]; >>>>>> >>>>>> Hmm.. If we only need to add one more 4 bytes field in struct node_v2, but >>>>>> V2_NSIZE is defined as fixed 500, there must be 492 bytes wasted. >>>>>> >>>>>> Or we can define V2_NSIZE as 8, but if there comes more and more extended >>>>>> fields, node version count can be a large number, it results in complicated >>>>>> version recognization and handling. >>>>>> >>>>>> One more question is how can we control which fields are valid or not in >>>>>> comp[Vx_NSIZE]? >>>>>> >>>>>> >>>>>> Anyway, what I'm thinking is maybe we can restructure layout of node block like >>>>>> the one used by f2fs_inode: >>>>>> >>>>>> struct f2fs_node { >>>>>> union { >>>>>> struct f2fs_inode i; >>>>>> union { >>>>>> struct { >>>>>> __le32 node_checksum; >>>>>> __le32 feature_field_1; >>>>>> __le32 feature_field_2; >>>>>> .... >>>>>> __le32 addr[]; >>>>>> >>>>>> }; >>>>>> struct direct_node dn; >>>>>> struct indirect_node in; >>>>>> }; >>>>>> }; >>>>>> struct node_footer footer; >>>>>> } __packed; >>>>>> >>>>>> Moving all extended fields to the head of f2fs_node, so we don't have to use >>>>>> macro to indicate actual size of addr. >>>>> >>>>> Thinking what'd be the best way. My concern is, once getting more entries, we >>>> >>>> OK, I think we need more discussion.. ;) >>>> >>>>> can't set each of features individually. Like the second entry should have >>>> >>>> Oh, that will be hard. If we have to avoid that, we have to tag in somewhere >>>> e.g. f2fs_inode::i_flags2 to indicate which new field in f2fs_node is valid, for >>>> example: >>>> >>>> #define F2FS_NODE_CHECKSUM 0x0001 >>>> #define F2FS_NODE_FIELD1 0x0002 >>>> #define F2FS_NODE_FIELD2 0x0004 >>>> >>>> union { >>>> struct { >>>> __le32 node_checksum; >>>> __le32 field_1; >>>> __le32 field_2; >>>> .... >>>> __le32 addr[]; >>>> }; >>>> struct direct_node dn; >>>> struct indirect_node in; >>>> }; >>>> >>>> f2fs_inode::i_flags2 = F2FS_NODE_CHECKSUM | F2FS_NODE_FIELD1 >>>> indicates that f2fs_node::node_checksum and f2fs_node::field_1 are valid; >>>> >>>> f2fs_inode::i_flags2 = F2FS_NODE_FIELD1 | F2FS_NODE_FIELD2 >>>> indicates that f2fs_node::field_1 and f2fs_node::field_2 are valid. >>> >>> So, that's why I thought we may need a sort of each formats. >> >> Hmm.. if we have two new added fields, there are (2 << 2) combinations >> of all formats, as: >> >> struct original { >> __le32 data[DEF_ADDRS_PER_BLOCK]; >> } >> >> struct node_v1 { >> __le32 data[DEF_ADDRS_PER_BLOCK - V1_NSIZE=1]; >> __le32 field_1; >> } >> >> struct node_v2 { >> __le32 data[DEF_ADDRS_PER_BLOCK - V2_NSIZE=1]; >> __le32 field_2; >> } >> >> struct node_v2 { >> __le32 data[DEF_ADDRS_PER_BLOCK - V3_NSIZE=2]; >> __le32 field_1; >> __le32 field_2; >> } >> >> If we add more new fields, the node version will increase sharply due >> to there is (n << 2) combination with n fields. Right? Any thoughts to >> reduce maintaining overhead on those node versions structures? > > Do you have time to explain more about the design of multiple version structure > for node block, I'm still be confused about two things: > 1. what will we do if we want to add one new field in node structure. > 2. how can we recognize which fields are valid and which ones are invalid. > > Thanks, > >> >> Thanks, >> >>> >>>> >>>> Any thoughts? >>>> >>>> Thanks, >>>> >>>>> enabled node_checksum, which we may not want to do. >>>>> >>>>>> >>>>>> Thanks, >>>>>> >>>>>>> __le32 comp[V2_NSIZE]; >>>>>>> } >>>>>>> ... >>>>>>> >>>>>>>> + }; >>>>>>>> + struct direct_node dn; >>>>>>>> + struct indirect_node in; >>>>>>>> + }; >>>>>>>> }; >>>>>>>> struct node_footer footer; >>>>>>>> } __packed; >>>>>>>> -- >>>>>>>> 2.15.0.55.gc2ece9dc4de6 >>>>>>> >>>>>>> . >>>>>>> >> >> . >> >