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Date: Wed, 23 May 2012 13:15:51 -0500
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From: Alan Cox <alan.l.cox@gmail.com>
To: Maksim Yevmenkin <maksim.yevmenkin@gmail.com>
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Subject: Re: RFC: [PATCH] disabling buckets under "low memory"
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On Wed, May 23, 2012 at 1:05 PM, Maksim Yevmenkin <
maksim.yevmenkin@gmail.com> wrote:

> hello,
>
> would anyone object to the following patch?
>
>
No objection.  There shouldn't be any controversy here.  Your patch is
correct.  The existing code in UMA is doing the wrong comparison.

Alan


> ===
>
> Index: uma_core.c
> ===================================================================
> --- uma_core.c  (revision 616)
> +++ uma_core.c  (working copy)
> @@ -267,10 +267,7 @@
>  static void
>  bucket_enable(void)
>  {
> -       if (cnt.v_free_count < cnt.v_free_min)
> -               bucketdisable = 1;
> -       else
> -               bucketdisable = 0;
> +       bucketdisable = vm_page_count_min();
>  }
>
> ===
>
> i've observed situation where per-cpu buckets were disabled while
> there were enough free cached pages. basically, cnt.v_free_count was
> sitting stable at a value lower than cnt.v_free_min and that caused
> massive performance drop. tuning down vm.v_free_min sysctl immediately
> helped.
>
> thanks,
> max
>