Hi, On Fri 19-03-10 08:53:08, Kailas Joshi wrote: > I am facing some problems while implementing alloc_on_commit. > While performing exhaustive write operations(for example using postmark), > system locks up after some time. > It runs fine for (simple)non-exhaustive write operations. > > I am using filemap_write_and_wait() in journal commit callback for > performing synchronous block allocation. It uses special journal handle > which enables use of early reservations. > Is it right to use this function here? If no, is there any other alternative > that should be used in this scenario? > > I am using following strategy - > 1) ext4_da_get_block_prep() marks delayed-allocation buffers with BH_DA > after reserving space for them. We have a BH_Delay flag for this already. OK, probably you need a temporary flag which you can clear in ext4_da_write_begin. I'd find counting number of BH_Delay buffers before and after block_write_begin call nicer... > 2) ext4_da_write_begin() counts the number of buffers marked with BH_DA and > reserves credits for block allocation. > 3) journal_stop() accumulates the unused credits of a handle in the > transaction. > 4) journal_start() when called with nblocks=0, creates a special handle with > the credits accumulated by all previous handles(by step 2). This is a hack. I'd rather create a separate JBD2 function for this. > 5) journal_commit() creates special handle for block allocation(as in step > 4) and calls filemap_write_and_wait() to perform block allocation. > > I am also sending the patch(for kernel 2.6.32.4) for my implementation (also > available at > http://www.cse.iitb.ac.in/~kailasjoshi/files/alloc_on_commit.patch). > > Being new to filesystem development, I am not able to identify the problem. > I will be very greatful if someone can help me out. Probably you are hitting some lock inversion problem. I suggest you compile the kernel with lockdep enabled (in Kernel hacking -> Lock debugging -> Prove lock correctness or something like that) and see whether it issues some warnings. If not, you can get backtraces of the locked up processes by pressing Alt-Sysrq-w (or echo "w" >/proc/sysrq-trigger). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
