[Bug 246886] [sendfile] Nginx + NFS or FUSE causes VM stall

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=246886

--- Comment #55 from Alan Somers <asomers at FreeBSD.org> ---
(In reply to Gleb Smirnoff from comment #54)
It's not likely that aio_read makes a difference, since he is seeing the
warning about "use unsafe AIO requests".  That warning means that aio_read
would've returned EOPNOTSUPP without doing anything.  UNLESS there's a bug in
aio(4) very high in the stack, before the safety check, that is leaking a
resource.

Background: "unsafe" AIO means operations where there is no guarantee that the
operation will ever complete, due to network unreliability (in your case), or
disk unreliability, if you're accessing a disk directly rather than a file
system.  I've never liked that seat belt, because it blocks so many of AIO's
best use cases.  You can disable it by setting vfs.aio.enable_unsafe=1 in
/etc/sysctl.conf.

I'm puzzled that disabling aio in NGinx makes a difference.  Could you please
repeat that experiment?  It shouldn't matter, if unsafe AIO is disabled and
you're serving from NFS or FUSE.

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