Messages in this thread | | | Subject | Re: [PATCH 2/2] f2fs: support {d,id,did,x}node checksum | From | Chao Yu <> | Date | Sat, 10 Feb 2018 10:52:18 +0800 |
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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?
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 >>>>> >>>>> . >>>>>
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