fuse: trying to steal weird page

[Nikolaus Rath <Nikolaus@rath.org>]

Hello,

I have recently noticed that a FUSE filesystem regularly produces many
kernel messages like this:

[ 2333.009931] fuse: trying to steal weird page
[ 2333.009937] fuse:   page=00000000dd1750e3 index=2022240 flags=17ffffc0000097, count=1, mapcount=0, mapping=00000000125079ad
[ 2334.595835] fuse: trying to steal weird page
[ 2334.595841] fuse:   page=000000009e8626ac index=2052288 flags=17ffffc0000097, count=1, mapcount=0, mapping=00000000125079ad
[ 2334.983568] fuse: trying to steal weird page
[ 2334.983572] fuse:   page=0000000013fdd9e4 index=2059392 flags=17ffffc0000097, count=1, mapcount=0, mapping=00000000125079ad
[ 2335.979905] fuse: trying to steal weird page
[ 2335.979911] fuse:   page=00000000a7057848 index=2078588 flags=17ffffc0000097, count=1, mapcount=0, mapping=00000000125079ad

They do not seem to correlate with userspace errors, but I noticed that
there is no significant performance difference between libfuse using
splice, splice with SPLICE_MOVE, and not using splice. This is somewhat
unexpected, so maybe it is related to the kernel messages?

What are the implications of the above kernel message? Is there a way to
provide more debugging information?

(I have reported a similar issue before
(https://marc.info/?l=linux-mm&m=155290847909996&w=2) and the patch may
not be present in the kernel that I'm using. However, the previous time
the warning had a different set of flags and a null mapping, so I think
this one is different).

$ uname -a
Linux valve 5.3.0-46-generic #38-Ubuntu SMP Fri Mar 27 17:37:05 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux


Best,
-Nikolaus


-- 
GPG Fingerprint: ED31 791B 2C5C 1613 AF38 8B8A D113 FCAC 3C4E 599F

             »Time flies like an arrow, fruit flies like a Banana.«