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From: Jakub Kicinski <>
To: Shakeel Butt <>
Cc: Andrew Morton <>,
	Linux MM <>, Kernel Team <>,
	Tejun Heo <>, Johannes Weiner <>,
	Chris Down <>,
	Cgroups <>,
	Michal Hocko <>
Subject: Re: [PATCH mm v3 3/3] mm: automatically penalize tasks with high swap use
Date: Mon, 18 May 2020 12:42:10 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, 17 May 2020 06:44:52 -0700 Shakeel Butt wrote:
> > Use one counter for number of pages allocated under pressure
> > to save struct task space and avoid two separate hierarchy
> > walks on the hot path.
> The above para seems out of place. It took some time to realize you
> are talking about current->memcg_nr_pages_over_high. IMO instead of
> this para, a comment in code would be much better.

Where would you like to see the comment? In struct task or where
counter is bumped?

> > Take the new high limit into account when determining if swap
> > is "full". Borrowing the explanation from Johannes:
> >
> >   The idea behind "swap full" is that as long as the workload has plenty
> >   of swap space available and it's not changing its memory contents, it
> >   makes sense to generously hold on to copies of data in the swap
> >   device, even after the swapin. A later reclaim cycle can drop the page
> >   without any IO. Trading disk space for IO.
> >
> >   But the only two ways to reclaim a swap slot is when they're faulted
> >   in and the references go away, or by scanning the virtual address space
> >   like swapoff does - which is very expensive (one could argue it's too
> >   expensive even for swapoff, it's often more practical to just reboot).
> >
> >   So at some point in the fill level, we have to start freeing up swap
> >   slots on fault/swapin.  
> swap.high allows the user to force the kernel to start freeing swap
> slots before half-full heuristic, right?

I'd say that the definition of full is extended to include swap.high.

  reply	other threads:[~2020-05-18 19:42 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15 20:20 [PATCH mm v3 0/3] memcg: Slow down swap allocation as the available space gets depleted Jakub Kicinski
2020-05-15 20:20 ` [PATCH mm v3 1/3] mm: prepare for swap over-high accounting and penalty calculation Jakub Kicinski
2020-05-15 20:20 ` [PATCH mm v3 2/3] mm: move penalty delay clamping out of calculate_high_delay() Jakub Kicinski
2020-05-15 20:20 ` [PATCH mm v3 3/3] mm: automatically penalize tasks with high swap use Jakub Kicinski
2020-05-17 13:44   ` Shakeel Butt
2020-05-18 19:42     ` Jakub Kicinski [this message]
2020-05-18 19:58       ` Shakeel Butt
2020-05-19  0:42     ` Jakub Kicinski
2020-05-19  1:10       ` Shakeel Butt

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