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[dm-devel] a problem when i use dm_io



hi, all
i am interested in facebook flashcache,which uses device mapper to make ssd as a disk cache, i want to add some functions in it, so i modify some codes. but when i use dm_io_async_bvec(1, &job->cache, WRITE,bio->bi_io_vec,bio->bi_idx, io_callback, kcached_job)  (the params is all right)submit a bio.
it does not call the io_callback function. i use systemtap to trace the function. the result like this:(sometimes is: enter dm_io_async_bvec; enter submit_bio; enter generic_make_request, generic_make_request return, submit_bio return, dm_io_async_bvec return.  sometimes is :enter dm_io_async_bvec; enter submit_bio; enter generic_make_request,  dm_io_async_bvec return) 
it do not know why, and why it did not call the io_callback.
 
thanks.
 
2011-12-01

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