linux-kernel - Re: [PATCH] mm:vmscan: shrink skip folios in the exiting task

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Date: Wed, 24 Jan 2024 13:20:46 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Zhiguo Jiang <justinjiang@...o.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, opensource.kernel@...o.com
Subject: Re: [PATCH] mm:vmscan: shrink skip folios in the exiting task

On Wed, Jan 24, 2024 at 08:43:07PM +0800, Zhiguo Jiang wrote:
> If the shrinking folio is belong to the exiting task, this folio should
> be freed in the task exit flow rather than being reclaimed in the shrink
> flow, because the former takes less time.
> 
> If the folio which is belong to the exiting task is reclaimed in the
> shrink flow, such as the anon folio, the anon folio needs to be first
> written to the swap partition by swap-in in shrink flow, and then the
> corresponding swap folio needs to be released in the task exiting flow.
> As is well known, releasing a swap folio will task more time than 
> releasing directly an anon folio.
> 
> In the scenarios of the low memory system and mutil backed-applications,
> the time-consuming problem caused by shrinking the exiting task's folios
> will be more severe.

What testing have you done of this patch?  How often does it happen?
Are there particular workloads that benefit from this?  (I'm not sure
what "mutil backed-applications" are?)

And I do mean specifically of this patch, because to my eyes it
shouldn't even compile.