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Date:      Tue, 02 Apr 2024 12:40:27 +0000
From:      bugzilla-noreply@freebsd.org
To:        fs@FreeBSD.org
Subject:   [Bug 275594] High CPU usage by arc_prune; analysis and fix
Message-ID:  <bug-275594-3630-IJdQv9hlhS@https.bugs.freebsd.org/bugzilla/>
In-Reply-To: <bug-275594-3630@https.bugs.freebsd.org/bugzilla/>
References:  <bug-275594-3630@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D275594

--- Comment #101 from Olivier Certner <olce@FreeBSD.org> ---
Hi Seigo,

Sorry, I had other things to look for in the meantime, so did not make much
progress up to now.  That said, from now on I should be able to work on it =
near
to full-time.

(In reply to Seigo Tanimura from comment #99)

That is my first target indeed.  Seems fairly simple.

(In reply to Seigo Tanimura from comment #100)

Great.

First of all, let me say I've never personally experienced the bug reported
here.  I'm using poudriere for big builds from time to time, and with ZFS, =
but
on machines with plenty of RAM, so that may explain why.  Bottom-line is th=
at I
don't have any reproducer on my own at the moment.  Will try to spin up som=
e VM
with a limited amount of RAM, limit the number of vnodes in the system and =
the
ARC, and see how that goes.

Second, it seems that this problem materializes enough and with enough seve=
rity
that it is quite urgent to find/commit fixes for it.  It might be that some=
 of
the changes proposed here cannot be imported as is because of subtle impact=
s or
design issues (I'm just saying this generally, this may not apply in the en=
d).=20
If it happens to be the case, we'll work on proposing alternatives easier to
review/get accepted, and defer the other changes.  Longer term, the vnode
recycling mechanism will probably be completely re-thinked, but hopefully t=
he
whole of it shouldn't be a requirement to solve the case at hand.

So, please bear a little with me until I get up to speed with all your patc=
hes
and results, and the reports of testers in this bug and some connected ones.

--=20
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