* add symlink force for unittest

* open unittest

* update, test=develop

Fix ops doc for some ops 

* split train_mode and has_grad

* fix format

* fix ci problems

* fix sample code

* add lars to fleet meta optimizer

* add lamb to proto

* add lamb to fleet meta optimizer

* fixed syntax bug

* fixed syntax bug

* fixed syntax error in lamb, add config setter of lamb in distributed_strategy

* trigger unitest to rerun

* add new unitest func for lamb

* revise unitest for lars and lamb

* revise dgc meta unitest

* revise lars document in distribute_strategy

* revise lars lamb document in distributed_strategy.py

* revise lars lamb document in distributed_strategy.py

* add weight decay exclude logic to lars

* restore optimzier.py

* restore optimizer.py as develop except lars

* add epsilon and exclude fn to distributed_sttrategy

* add lars epsilon

* revise unitest for fleet lars and lamb

* revise lars lamb unitest for CI coverage

* revise lars argument api

* revise lars argument api

* revise lars argument api

* revise api doc of lars

* fix op role

* add sharding save and add_sync_comm_for_test function

* add comm_analyse to utlis

* revise sharding_utils

* add sharding saving unittest

* revise sharding utils for unittest

* revise sharding en doc

* update sharding utils api

* add doc for sharding

* fixed bug in sharding var size count

* update varsize count in sharding

* fix sharding num_nccl_comm

* Revert "fix sharding num_nccl_comm"

This reverts commit d51587c15e9323acf226ddd36154275f0d1daf76.

* add static_only for static api

* addd static_only for class init

* remove static_only for default_main_program

* remove creater_parameter & startup_program

* remove failed apis

* revert py_func import

* remove global scope

* remove some api

* remove cuda pinned place

* fix examples, test=document_fix

* fix, test=document_fix

add API serialize_program, serialize_persistables, save_to_file, deserialize_program, deserialize_persistables, load_from_file. (#29034)

* remove BatchSampler type check. test=develop

* Add bf16 pool2d and unify bf16 unit tests

* Add change default ops test

* default not show cpp statck & add hint

* fix failed unittest

* fix failed unittests

* Fix doc format for callbacks, metrics and Model
* Fix code sample and doc

* change load dict file one by one to warn

* add unittests for coverage

* polish error message

* fix cond error

* Rename variables when use 'jit.load'

* Check whether the original graph contains the variable with the same name

* add comment

* rename output/input of op and edit unittest

* modify the code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* edit code according to CI

* fix syncbn

* add unittest

add uint8 for reshape operator

* Support pop for dict in dy2stat

* Move convert_pop to convert_operators.py and polish convert_pop

* fix tensor detach to zero copy

* fix tensor detach to zero copy

* add reminder of fluid.layers.lstm

* Impelement 2.0 API version Conv2d and Linear layer quantization in imperative mode.

* use cudnn softmax in static Lenet

* Modified ChannelwiseQAT Unittest for 2.0 API.

* For CI python coverage.

* polish parallel api impl & doc details

* add unittest for coverage

* remove spawn test in py2.7

* add parallel api into white list

As the title

* add soft_label and axis for CrossEntropyLoss and improve performance,test=develop

* fix conflict in nn/functional/loss.py, test=develop

* fix some docs test=develop;test=document_fix

* add code example test=develop;test=document_fix

* fix code example test=develop;test=document_fix

* fix code example test=develop;test=document_fix

* fix code example test=develop;test=document_fix