Re: [f2fs-dev] [PATCH] f2fs: change virtual mapping way for compression pages

[Daeho Jeong <daeho43@gmail.com>]

Plus, when we use vmap(), vmap() normally executes in a short time
like vm_map_ram().
But, sometimes, it has a very long delay.

2020년 8월 11일 (화) 오후 6:28, Daeho Jeong <daeho43@gmail.com>님이 작성:
>
> Actually, as you can see, I use the whole zero data blocks in the test file.
> It can maximize the effect of changing virtual mapping.
> When I use normal files which can be compressed about 70% from the
> original file,
> The vm_map_ram() version is about 2x faster than vmap() version.
>
> 2020년 8월 11일 (화) 오후 4:55, Chao Yu <yuchao0@huawei.com>님이 작성:
> >
> > On 2020/8/11 15:15, Gao Xiang wrote:
> > > On Tue, Aug 11, 2020 at 12:37:53PM +0900, Daeho Jeong wrote:
> > >> From: Daeho Jeong <daehojeong@google.com>
> > >>
> > >> By profiling f2fs compression works, I've found vmap() callings are
> > >> bottlenecks of f2fs decompression path. Changing these with
> > >> vm_map_ram(), we can enhance f2fs decompression speed pretty much.
> > >>
> > >> [Verification]
> > >> dd if=/dev/zero of=dummy bs=1m count=1000
> > >> echo 3 > /proc/sys/vm/drop_caches
> > >> dd if=dummy of=/dev/zero bs=512k
> > >>
> > >> - w/o compression -
> > >> 1048576000 bytes (0.9 G) copied, 1.999384 s, 500 M/s
> > >> 1048576000 bytes (0.9 G) copied, 2.035988 s, 491 M/s
> > >> 1048576000 bytes (0.9 G) copied, 2.039457 s, 490 M/s
> > >>
> > >> - before patch -
> > >> 1048576000 bytes (0.9 G) copied, 9.146217 s, 109 M/s
> > >> 1048576000 bytes (0.9 G) copied, 9.997542 s, 100 M/s
> > >> 1048576000 bytes (0.9 G) copied, 10.109727 s, 99 M/s
> > >>
> > >> - after patch -
> > >> 1048576000 bytes (0.9 G) copied, 2.253441 s, 444 M/s
> > >> 1048576000 bytes (0.9 G) copied, 2.739764 s, 365 M/s
> > >> 1048576000 bytes (0.9 G) copied, 2.185649 s, 458 M/s
> > >
> > > Indeed, vmap() approach has some impact on the whole
> > > workflow. But I don't think the gap is such significant,
> > > maybe it relates to unlocked cpufreq (and big little
> > > core difference if it's on some arm64 board).
> >
> > Agreed,
> >
> > I guess there should be other reason causing the large performance
> > gap, scheduling, frequency, or something else.
> >
> > >
> > >
> > >
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> > > .
> > >