On Tue, Jul 16, 2013 at 11:14:29AM -0400, sheng qiu wrote: > Hi Kent, > > sorry to bother you again. i got another question. it's about the > bucket->pin. Can you explain what's the usage for this data member? > i see only bucket with pin value "0" can be invalidated. And only "0" > valued pin bucket's prio will be decreased within the > bch_rescale_priorities(). But every time when you write data to > bucket, you increase that bucket's pin, and i did not see when it will > be decreased. This makes me a little confused. Or do i miss anything > where you might reset it?
It's to keep buckets from being garbage collected after they're allocated but before we've added a pointer to them to the btree. I've actually been meaning to get rid of it, and just keep a refcount on the open buckets (the ones pick_data_bucket() uses) and have garbage collection mark those buckets too. Originally I also used it for preventing buckets from being invalidated while we were reading from them (on cache hit), but I got rid of that ages ago for performance reasons - now it just checks after the read finishes if it was invalidated, and if so rereads from the backing device. -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
