On Wed, Jan 11, 2017 at 10:49:03AM -0800, Song Liu wrote: > Chunk aligned read significantly reduces CPU usage of raid456. > However, it is not safe to fully bypass the write back cache. > This patch enables chunk aligned read with write back cache. > > For chunk aligned read, we track stripes in write back cache at > a bigger granularity, "big_stripe". Each chunk may contain more > than one stripe (for example, a 256kB chunk contains 64 4kB-page, > so this chunk contain 64 stripes). For chunk_aligned_read, these > stripes are grouped into one big_stripe, so we only need one lookup > for the whole chunk. > > For each big_stripe, struct big_stripe_info tracks how many stripes > of this big_stripe are in the write back cache. We count how many > stripes of this big_stripe are in the write back cache. These > counters are tracked in a radix tree (big_stripe_tree). > r5c_tree_index() is used to calculate keys for the radix tree. > > chunk_aligned_read() calls r5c_big_stripe_cached() to look up > big_stripe of each chunk in the tree. If this big_stripe is in the > tree, chunk_aligned_read() aborts. This look up is protected by > rcu_read_lock(). Hmm, this is still not fixed yet. Need the spin_lock to protect the look up. Also correct commnets should be : /* * something */ There are several places you didn't get it right, please fix Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
