Hi Pony Cheng-- On 01/28/2018 11:23 PM, Pony Cheng wrote: > Hi all: > I'm reading the source code of bcache, and I'm so confused about > journal. Journal just use bucket of cache, why we need it, and what's > the real purpose of journal in bcache. If we write to the bucket, do > we need write it to journal first? The purpose of the journal is to control write amplification from btree node writes. If we have 100 things to insert into the btree because we're just caching new things, and this would touch 100 different btree nodes, we can just write the new nodes to the journal in a single I/O instead of doing 100 different updates. Later, we can free the journal pages by doing those updates, but hopefully be doing more than one update to each btree node and significantly lessen the total amount of I/O. > > How do you think of these? > > Pony Cheng Regards, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
