linux-kernel - Re: [PATCH] mm: workingset: clarify eviction order and distance calculation

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Date:   Thu, 11 Feb 2021 22:26:45 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     akpm@...ux-foundation.org
Cc:     hannes@...xchg.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: workingset: clarify eviction order and distance
 calculation

On Mon, Feb 01, 2021 at 07:06:51AM +0100, Oscar Salvador wrote:
> The premise of the refault distance is that it can be seen as a deficit
> of the inactive list space, so that if the inactive list would have had
> (R - E) more slots, the page would not have been evicted but promoted
> to the active list instead.
> 
> However, the way the code is ordered right now set us to be off by one,
> so the real number of slots would be (R - E) + 1.
> I stumbled upon this when trying to understand the code and it puzzled me
> that the comments did not match what the code did.
> 
> This it not an issue at all since evictions and refaults tend to happen
> in a number large enough that being off-by-one does not have any impact
> - and since the compiler and CPUs are free to rearrange the execution
> sequence anyway.
> But as Johannes says, it is better to re-arrange the code in the proper
> order since otherwise would be misleading to somebody who is actively
> reading and trying to understand the logic of the code - like it
> happened to me.
> 
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
> Acked-by: Johannes Weiner <hannes@...xchg.org>

Hi Andrew,

is this on your radar?

Thanks!

-- 
Oscar Salvador
SUSE L3