Hi list, In this thread[1], I found a defect in jbd2 because it needs two wrties to finish a transacation because it writes journal header and data to disk and it will write commit to disk after above writes are done. AFAIK, in jbd2, it will call submit_bh twice at least to write the data because journal header, data and commit are stored in different buffer_heads. If we don't call them separately, these calls might be out of order. Obviously, it must ensure that journal header and data are written before commit. But this brings a huge overhead in this benchmark[2]. So, IMHO, if we could use *bio* to store these data rather than buffer_head, we could avoid this overhead because we can call submit_bio only once to write all of data, which contains journal header, data and commit. Here is an issue that I don't determine. If we use submit_bio to write journal data, it will make all of data with WRITE_FLUSH_FUA flag. But now there is only commit data with this flag. I am not sure whether or not it brings some other unpridictable problems. :( Please feel free to comment this RFC. Thank you. 1. http://www.spinics.net/lists/linux-ext4/msg31637.html 2. benchmark: time for((i=0;i<2000;i++)); do \ dd if=/dev/zero of=/mnt/sda1/testfile conv=notrunc bs=4k \ count=1 seek=`expr $i \* 16` oflag=sync,direct 2>/dev/null; \ done Regards, Zheng -- 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
