On 01/03/2018 06:03 AM, Coly Li wrote: > Member devices of struct cache_set is used to reference all attached > bcache devices to this cache set. If it is treated as array of pointers, > size of devices[] is indicated by member nr_uuids of struct cache_set. > > nr_uuids is calculated in drivers/md/super.c:bch_cache_set_alloc(), > bucket_bytes(c) / sizeof(struct uuid_entry) > Bucket size is determined by user space tool "make-bcache", by default it > is 1024 sectors (defined in bcache-tools/make-bcache.c:main()). So default > nr_uuids value is 4096 from the above calculation. > > Every time when bcache code iterates bcache devices of a cache set, all > the 4096 pointers are checked even only 1 bcache device is attached to the > cache set, that's a wast of time and unncessary. > > This patch adds a member devices_max_used to struct cache_set. Its value > is 1 + the maximum used index of devices[] in a cache set. When iterating > all valid bcache devices of a cache set, use c->devices_max_used in > for-loop may reduce a lot of useless checking. > > Personally, my motivation of this patch is not for performance, I use it > in bcache debugging, which helps me to narrow down the scape to check > valid bcached devices of a cache set. Oh, OK. I was going to argue that I didn't think this was worth it, but I can see how it would be nice for inspecting memory and debug code. > > Signed-off-by: Coly Li <colyli@xxxxxxx> Reviewed-by: Michael Lyle <mlyle@xxxxxxxx>
