on 3/17/2023 11:50 PM, Theodore Ts'o wrote: > On Thu, Mar 16, 2023 at 06:19:40PM +0800, Kemeng Shi wrote: >> Hi Theodore, thanks for feedback. I will submit another patchset for >> mballoc and I would like to include this fix if no one else does. As >> new patches may be conflicted with old ones I submited, I would submit >> the new patchset after the old ones are fully reviewed and applied >> if this fix is not in rush. Thanks! > > Hi, I've already taken the your patches into the dev branch; were > there any changes you were intending to make to your patches? > > If you could submit a separate fix for the bug that I noticed, that > would be great. Hi, I was stuck in some urgent work recently and I will do this ASAP and it should be done in this week. > Also, if you are interested in doing some more work in mballoc.c, I > was wondering if you would be interested in adding some Kunit tests > for mballoc.c. A simple example Kunit test for ext4 can be found in > fs/ext4/inode_test.c. (The convention is to place tests for foo.c in > foo_test.c.) > [1] https://docs.kernel.org/dev-tools/kunit/ > > In order to add mballoc Kunit tests, we will need to add some "mock"[2] > functions to simulate what happens when mballoc.c tries reading a > block bitmap. My thinking was to have a test provide an array of some > data structure like this: > > struct test_bitmap { > unsigned int start; > unsigned int len; > }; > > [2] https://en.wikipedia.org/wiki/Mock_object > > ... which indicates the starting block, and the length of a run of > blocks that are marked as in use, where the list of blocks are sorted > by starting block number, and where a starting block of ~0 indicates > the end of the list of block extents. > We would also need have a set of utility ext4 Kunit functions to > create "fake" ext4 superblocks and ext4_sb_info structures. The Kunit tests thing sounds interesting and I would like to this. But I still need some time to get basic knowledge then I maybe able to discuss detais. Of couse, anyone is also interesting in this and can make this work soon is fine.:) > I was originally thinking that obvious starting Kunit tests would be > for fs/ext4/hash.c and fs/ext4/extents_status.c, since they require > the little or no "mocking" support. However, there are so many > changes in fs/ext4/mballoc.c, the urgency in having unit tests for it > is getting more urgent --- since if there is a bug in one of these > functions, such as the one that I noted in > ext4_mb_new_blocks_simple(), since it's harder to exhaustively test > some of these smaller sub-functions in integration tests such as those > found in xfstests. Unit tests are the best way to make sure we're > testing all of the code paths in a complex module such as mballoc.c Yes, I can't agree more and this may be able to find other exsiting bugs. -- Best wishes Kemeng Shi
