On (04/26/17 09:52), js1...@gmail.com wrote:
[..]
> +struct zram_hash {
> + spinlock_t lock;
> + struct rb_root rb_root;
> };
just a note.
we can easily have N CPUs spinning on ->lock for __zram_dedup_get() lookup,
which can invole a potentially slow zcomp_decompress() [zlib, for example,
with 64k pages] and memcmp(). the larger PAGE_SHIFT is, the more serialized
IOs become. in theory, at least.
CPU0 CPU1 ... CPUN
__zram_bvec_write() __zram_bvec_write() __zram_bvec_write()
zram_dedup_find() zram_dedup_find() zram_dedup_find()
spin_lock(&hash->lock);
spin_lock(&hash->lock);
spin_lock(&hash->lock);
__zram_dedup_get()
zcomp_decompress()
...
so may be there is a way to use read-write lock instead on spinlock for hash
and reduce write/read IO serialization.
-ss
