Messages in this thread | | | Date | Wed, 26 Apr 2017 13:28:26 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [PATCH v4 2/4] zram: implement deduplication in zram |
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On (04/26/17 09:52), js1304@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
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