Hi Kent, i do not know if this is a problem or i did not understand correctly. when i enable the copy_gc, at first the gc_moving_threshold is larger than the bucket size (512KB), i guess maybe initially they are set to 1<<14 -1, after some time, seems all the bucket are set to use all the sectors it own, which is 1024 in my case. I guess this is because SET_GC_SECTORS_USED(bucket.size) is called while returning a free bucket for new allocation. then the gc_moving_threshold became 1024 (512KB), and no bucket's GC_SECTORS_USED is smaller than this value. So no gc_moving event at all. at first, i thought the bcache code would set 0 sectors used for each new allocated bucket, and then update GC_SECTORS_USED whenever fill data into the bucket. In that way, we can track how many data are valid within a bucket. Do i misunderstanding anything? i am a little confused. Thanks, Sheng On Wed, Jul 10, 2013 at 10:16 PM, sheng qiu <herbert1984106@xxxxxxxxx> wrote: > i see. Thanks a lot for your explain. i have some further questions > below, i will be appreciated if you have time to answer. > > by "arbitrary number", can i understand it as the user can decide how > many keys in the keybuf or something else? > when the keybuf code try to refill itself, it continues scan following > "last_scan" or it start over from the beginning? if try to scan all > the existing keys per round, will it be very costly? > > Thanks, > Sheng > > > > > On Wed, Jul 10, 2013 at 7:02 PM, Kent Overstreet <kmo@xxxxxxxxxxxxx> wrote: >> On Wed, Jul 10, 2013 at 05:14:49PM -0400, sheng qiu wrote: >>> Hi Kent, >>> >>> i am sorry to bother you again. i am reading the movinggc.c, i am >>> really interested in this piece of codes. So if i enable the copy_gc, >>> this piece of codes will be active. My question is after the gc_moving >>> confirmed the gc_moving_threshold, it began to scan the bkeys. i do >>> not quite understand how you fill the moving_gc_keys, do you go >>> through all the current btree nodes to find proper keys for migration >>> (the bucket.used_sectors < threshold)? or you do incremental scans? >> >> Incremental scans - the keybuf code scans the btree until it has some >> arbitrary number of keys in a red black tree; the copy gc code pulls >> keys out of that one at a time to move them and the keybuf code refills >> itself by scanning incrementally as needed. > > > > -- > Sheng Qiu > Texas A & M University > Room 332B Wisenbaker > email: herbert1984106@xxxxxxxxx > College Station, TX 77843-3259 -- Sheng Qiu Texas A & M University Room 332B Wisenbaker email: herbert1984106@xxxxxxxxx College Station, TX 77843-3259 -- 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
