linux-kernel - Re: [PATCH v3] mm: pcp: increase pcp->free_count threshold to trigger free

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Message-ID: <20250512065038.22917-1-nikhil.dhama@amd.com>
Date: Mon, 12 May 2025 12:20:38 +0530
From: Nikhil Dhama <nikhil.dhama@....com>
To: <akpm@...ux-foundation.org>
CC: <bharata@....com>, <huang.ying.caritas@...il.com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <lkp@...el.com>,
	<mgorman@...hsingularity.net>, <nikhil.dhama@....com>,
	<oe-lkp@...ts.linux.dev>, <raghavendra.kt@....com>,
	<ying.huang@...ux.alibaba.com>
Subject: Re: [PATCH v3] mm: pcp: increase pcp->free_count threshold to trigger free_high

Hi Andrew, 

On 5/11/2025 10:00 AM, Andrew Morton wrote:
> On Mon, 28 Apr 2025 10:30:47 +0530 Nikhil Dhama <nikhil.dhama@....com> wrote:
>
>>> Nikhil's attentions are presumably elsewhere.  Could someone (Ying or
>>> Raghavendra?) please send along altered changelog text which I can
>>> paste in there?
>>
>> Please find the updated changelog text as follows:
>
> As far as I can tell, this replacement text is identical to that of the
> orginal patch.
>

As per Ying's suggestion following changes were made to changelog:

In para 1, 

> free_factor by 1 only when we try to reduce the size of pcp list or
> flush for high order, and free_high used to trigger only
> for order > 0 and order < costly_order and pcp->free_factor > 0.

removed "or flush for high order", updating it as 

> free_factor by 1 only when we try to reduce the size of pcp list and
> free_high used to trigger only for order > 0 and order < costly_order
> and pcp->free_factor > 0. 


In para 8, added idea suggested by Ying [1] behind changing the threshold 
from "batch" to  "batch + pcp->high_min / 2". Changed it from, 

> So, in this patch, we increased the pcp->free_count threshold to 
> trigger free_high from "batch" to "batch + pcp->high_min / 2". 

to 

> So, in this patch, we increased the pcp->free_count threshold to
> trigger free_high from "batch" to "batch + pcp->high_min / 2" as
> suggested by Ying [1], In the original pcp->free_factor solution,
> free_high is triggered for contiguous freeing with size ranging from
> "batch" to "pcp->high + batch".  So, the average value is "batch +
> pcp->high / 2".  While in the pcp->free_count solution, free_high will
> be triggered for contiguous freeing with size "batch".  So, to restore
> the original behavior, we can use the threshold "batch + pcp->high_min
> / 2"
[...]
> Link: https://lore.kernel.org/all/875xjmuiup.fsf@DESKTOP-5N7EMDA/ [1]

You seem to already have updated copy in mm tree from the email where I
missed to add linux-mm.

Thanks,
Nikhil