On Fri, 2014-05-30 at 16:34 +0800, Weijie Yang wrote: > Currently, we use a rwlock tb_lock to protect concurrent access to > the whole zram meta table. However, according to the actual access model, > there is only a small chance for upper user to access the same table[index], > so the current lock granularity is too big. > > The idea of optimization is to change the lock granularity from whole > meta table to per table entry (table -> table[index]), so that we can > protect concurrent access to the same table[index], meanwhile allow > the maximum concurrency. > With this in mind, several kinds of locks which could be used as a > per-entry lock were tested and compared: > > Test environment: > x86-64 Intel Core2 Q8400, system memory 4GB, Ubuntu 12.04, > kernel v3.15.0-rc3 as base, zram with 4 max_comp_streams LZO. > > iozone test: > iozone -t 4 -R -r 16K -s 200M -I +Z > (1GB zram with ext4 filesystem, take the average of 10 tests, KB/s) > > Test base CAS spinlock rwlock bit_spinlock > ------------------------------------------------------------------- > Initial write 1381094 1425435 1422860 1423075 1421521 > Rewrite 1529479 1641199 1668762 1672855 1654910 > Read 8468009 11324979 11305569 11117273 10997202 > Re-read 8467476 11260914 11248059 11145336 10906486 > Reverse Read 6821393 8106334 8282174 8279195 8109186 > Stride read 7191093 8994306 9153982 8961224 9004434 > Random read 7156353 8957932 9167098 8980465 8940476 > Mixed workload 4172747 5680814 5927825 5489578 5972253 > Random write 1483044 1605588 1594329 1600453 1596010 > Pwrite 1276644 1303108 1311612 1314228 1300960 > Pread 4324337 4632869 4618386 4457870 4500166 > > To enhance the possibility of access the same table[index] concurrently, > set zram a small disksize(10MB) and let threads run with large loop count. > > fio test: > fio --bs=32k --randrepeat=1 --randseed=100 --refill_buffers > --scramble_buffers=1 --direct=1 --loops=3000 --numjobs=4 > --filename=/dev/zram0 --name=seq-write --rw=write --stonewall > --name=seq-read --rw=read --stonewall --name=seq-readwrite > --rw=rw --stonewall --name=rand-readwrite --rw=randrw --stonewall > (10MB zram raw block device, take the average of 10 tests, KB/s) > > Test base CAS spinlock rwlock bit_spinlock > ------------------------------------------------------------- > seq-write 933789 999357 1003298 995961 1001958 > seq-read 5634130 6577930 6380861 6243912 6230006 > seq-rw 1405687 1638117 1640256 1633903 1634459 > rand-rw 1386119 1614664 1617211 1609267 1612471 > > All the optimization methods show a higher performance than the base, > however, it is hard to say which method is the most appropriate. > > On the other hand, zram is mostly used on small embedded system, so we > don't want to increase any memory footprint. > > This patch pick the bit_spinlock method, pack object size and page_flag > into an unsigned long table.value, so as to not increase any memory > overhead on both 32-bit and 64-bit system. > > On the third hand, even though different kinds of locks have different > performances, we can ignore this difference, because: > if zram is used as zram swapfile, the swap subsystem can prevent concurrent > access to the same swapslot; > if zram is used as zram-blk for set up filesystem on it, the upper filesystem > and the page cache also prevent concurrent access of the same block mostly. > So we can ignore the different performances among locks. > > Changes since v1: https://lkml.org/lkml/2014/5/5/1 > - replace CAS method with bit_spinlock method > - rename zram_test_flag() to zram_test_zero() > - add some comments > > Changes since v2: https://lkml.org/lkml/2014/5/15/113 > - change size type from int to size_t in zram_set_obj_size() > - refactor zram_set_obj_size() to make it readable > - add comments > > Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx> Reviewed-by: Davidlohr Bueso <davidlohr@xxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>