Strange ARC/Swap/CPU on yesterday's -CURRENT

[Cy Schubert]

Try arbitrarily reducing arc_max through sysctl. ARC is immediately reduced and free memory increased however wired pages remains the same.

---
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Cy Schubert
<Cy.Schubert at cschubert.com> or <cy at freebsd.org>
The need of the many outweighs the greed of the few.
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-----Original Message-----
From: Larry Rosenman
Sent: 03/04/2018 19:27
To: Cy Schubert; Bryan Drewery; Peter Jeremy; Jeff Roberson
Cc: FreeBSD current; Andriy Gapon
Subject: Re: Strange ARC/Swap/CPU on yesterday's -CURRENT

When my full backups run (1st Sunday -> Monday of the month) the box becomes unusable after 5-10 hours of that backup with LOTS of SWAP usage
And ARC using 100+G. 

Is anyone looking into this?



-- 
Larry Rosenman                     http://www.lerctr.org/~ler
Phone: +1 214-642-9640                 E-Mail: ler at lerctr.org
US Mail: 5708 Sabbia Drive, Round Rock, TX 78665-2106
On 4/3/18, 8:24 PM, "Cy Schubert" <owner-freebsd-current at freebsd.org on behalf of Cy.Schubert at cschubert.com> wrote:

    +1
    
    However under certain circumstances it will release some memory. To reproduce, when bsdtar unpacks some tarballs (when building certain ports) tar will use 12 GB or  more  forcing ARC to release memory.
    
    BTW, I haven't stopped to grok whether the bsdtar issue is local to me or another problem yet.
    
    ---
    Sent using a tiny phone keyboard.
    Apologies for any typos and autocorrect.
    Also, this old phone only supports top post. Apologies.
    
    Cy Schubert
    <Cy.Schubert at cschubert.com> or <cy at freebsd.org>
    The need of the many outweighs the greed of the few.
    ---
    
    -----Original Message-----
    From: Bryan Drewery
    Sent: 23/03/2018 17:23
    To: Peter Jeremy; Jeff Roberson
    Cc: FreeBSD current; Andriy Gapon
    Subject: Re: Strange ARC/Swap/CPU on yesterday's -CURRENT
    
    On 3/20/2018 12:07 AM, Peter Jeremy wrote:
    > 
    > On 2018-Mar-11 10:43:58 -1000, Jeff Roberson <jroberson at jroberson.net> wrote:
    >> Also, if you could try going back to r328953 or r326346 and let me know if 
    >> the problem exists in either.  That would be very helpful.  If anyone is 
    >> willing to debug this with me contact me directly and I will send some 
    >> test patches or debugging info after you have done the above steps.
    > 
    > I ran into this on 11-stable and tracked it to r326619 (MFC of r325851).
    > I initially got around the problem by reverting that commit but either
    > it or something very similar is still present in 11-stable r331053.
    > 
    > I've seen it in my main server (32GB RAM) but haven't managed to reproduce
    > it in smaller VBox guests - one difficulty I faced was artificially filling
    > ARC.
    > 
    
    Looking at the ARC change you referred to from r325851
    https://reviews.freebsd.org/D12163, I am convinced that ARC backpressure
    is completely broken. On my 78GB RAM system with ARC limited to 40GB and
    doing a poudriere build of all LLVM and GCC packages at once in tmpfs I
    can get swap up near 50GB and yet the ARC remains at 40GB through it
    all.  It's always been slow to give up memory for package builds but it
    really seems broken right now.
    
    -- 
    Regards,
    Bryan Drewery
    
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