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Message-ID: <56A29AE3.8090606@gmail.com>
Date: Fri, 22 Jan 2016 22:10:59 +0100
From: Jakob Unterwurzacher <jakobunt@...il.com>
To: linux-kernel@...r.kernel.org
Subject: Regression for mmap writes through FUSE in 4.2+
I have noticed an annoying regression that was introduced in 4.2 and is
still there in 4.4. mmap writes to FUSE filesystems are throttled down
to basically zero.
Reproducer: https://github.com/rfjakob/mmapwrite , testing against encfs:
$ mmapwrite /tmp/encfs-mnt/foo
1 .................................................. 107.01 MB/s
2 .................................................. 101.98 MB/s
[...]
68 .................................................. 106.79 MB/s
69 .................................................. 105.09 MB/s
70 .................................................. 2.02 MB/s
71 .................................................. 1.77 MB/s
72 .................................................. 0.42 MB/s
73 .................................... (hangs)
I have tested kernels from 4.0 and this seems to have been introduced in
4.2:
4.0 ....... 140MB/s permanent
4.1 ....... 140MB/s permanent
4.2 ....... 100MB/s at the start, sudden slowdown to 1MB/s after ~5GB
4.3 ....... 100MB/s at the start, sudden slowdown to 1MB/s after ~1.5GB
4.4-rc4 ... 100MB/s at the start, slowly ramps down, 0.3MB/s after ~2GB
4.4 ....... 100MB/s at the start, sudden slowdown after ~3GB
Is there a way to disable the throttling? Or at least exempt FUSE until
there is a proper fix?
Thanks,
Jakob
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