Re: [PATCH] zram: remove global tb_lock by using lock-free CAS
From: Minchan Kim
Date: Mon May 12 2014 - 01:12:52 EST
On Sat, May 10, 2014 at 02:10:08PM +0800, Weijie Yang wrote:
> On Thu, May 8, 2014 at 2:24 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> > On Wed, May 07, 2014 at 11:52:59PM +0900, Joonsoo Kim wrote:
> >> >> Most popular use of zram is the in-memory swap for small embedded system
> >> >> so I don't want to increase memory footprint without good reason although
> >> >> it makes synthetic benchmark. Alhought it's 1M for 1G, it isn't small if we
> >> >> consider compression ratio and real free memory after boot
> >>
> >> We can use bit spin lock and this would not increase memory footprint for 32 bit
> >> platform.
> >
> > Sounds like a idea.
> > Weijie, Do you mind testing with bit spin lock?
>
> Yes, I re-test them.
> This time, I test each case 10 times, and take the average(KS/s).
> (the test machine and method are same like previous mail's)
>
> Iozone test result:
>
> 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
>
> Fio test result:
>
> 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
>
>
> The base is v3.15.0-rc3, the others are per-meta entry lock.
> Every optimization method shows higher performance than the base, however,
> it is hard to say which method is the most appropriate.
It's not too big between CAS and bit_spinlock so I prefer general method.
>
> To bit_spinlock, the modified code is mainly like this:
>
> +#define ZRAM_FLAG_SHIFT 16
> +
> enum zram_pageflags {
> /* Page consists entirely of zeros */
> - ZRAM_ZERO,
> + ZRAM_ZERO = ZRAM_FLAG_SHIFT + 1,
> + ZRAM_ACCESS,
>
> __NR_ZRAM_PAGEFLAGS,
> };
>
> /* Allocated for each disk page */
> struct table {
> unsigned long handle;
> - u16 size; /* object size (excluding header) */
> - u8 flags;
> + unsigned long value;
Why does we need to change flags and size "unsigned long value"?
Couldn't we use existing flags with just adding new ZRAM_TABLE_LOCK?
> } __aligned(4);
>
> The lower ZRAM_FLAG_SHIFT bits of table.value is size, the higher bits
> is for zram_pageflags. By this means, it doesn't increase any memory
> overhead on both 32-bit and 64-bit system.
>
> Any complaint or suggestions are welcomed.
Anyway, I'd like to go this way.
Pz, resend formal patch with a number.
Thanks!
>
> >>
> >> Thanks.
> >>
> >> --
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> >
> > --
> > Kind regards,
> > Minchan Kim
>
>
> --
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--
Kind regards,
Minchan Kim
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