linux-kernel - Re: [PATCH 0/4] SLUB: calculate

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Date:   Mon, 2 Oct 2023 14:38:31 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     jaypatel@...ux.ibm.com, David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Roman Gushchin <roman.gushchin@...ux.dev>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] SLUB: calculate_order() cleanups

On 9/28/23 06:46, Jay Patel wrote:
> On Fri, 2023-09-08 at 16:53 +0200, Vlastimil Babka wrote:
>> Since reviewing recent patches made me finally dig into these
>> functions
>> in details for the first time, I've also noticed some opportunities
>> for
>> cleanups that should make them simpler and also deliver more
>> consistent
>> results for some corner case object sizes (probably not seen in
>> practice). Thus patch 3 can increase slab orders somewhere, but only
>> in
>> the way that was already intended. Otherwise it's almost no
>> functional
>> changes.
>> 
> Hi Vlastimil,

Hi, Jay!

> This cleanup patchset looks promising.
> I've conducted test
> on PowerPC with 16 CPUs and a 64K page size, and here are the results.
> 
> S
> lub Memory Usage
> 
> +-------------------+--------+------------+
> |                   | Normal | With Patch |
> +-------------------+--------+------------+
> | Total Slub Memory | 476992 | 478464     |
> | Wastage           | 431    | 451        |
> +-------------------+--------+------------+
> 
> Also, I have not detected any changes in the page order for slub caches
> across all objects with 64K page size.

As expected. Which should mean any benchmark differences should be noise and
not caused by the patches.

> Hackbench Results
> 
> +-------+----+---------+------------+----------+
> |     
>   |    | Normal  | With Patch |          |
> +-------+----+---------+-----
> -------+----------+
> | Amean | 1  | 1.1530  | 1.1347     | ( 1.59%) |
> |
> Amean | 4  | 3.9220  | 3.8240     | ( 2.50%) |
> | Amean | 7  | 6.7943  |
> 6.6300     | ( 2.42%) |
> | Amean | 12 | 11.7067 | 11.4423    | ( 2.26%) |
> | Amean | 21 | 20.6617 | 20.1680    | ( 2.39%) |
> | Amean | 30 | 29.4200
> | 28.6460    | ( 2.63%) |
> | Amean | 48 | 47.2797 | 46.2820    | ( 2.11%)
> |
> | Amean | 64 | 63.4680 | 62.1813    | ( 2.03%) |
> +-------+----+------
> ---+------------+----------+  
> 
> 
> Reviewed-by: Jay Patel
> <jaypatel@...ux.ibm.com>
> Tested-by: Jay Patel <jaypatel@...ux.ibm.com>

Thanks! Applied your Reviewed-and-tested-by:

> Th
> ank You 
> Jay Patel
>> Vlastimil Babka (4):
>>   mm/slub: simplify the last resort slab order calculation
>>   mm/slub: remove min_objects loop from calculate_order()
>>   mm/slub: attempt to find layouts up to 1/2 waste in
>> calculate_order()
>>   mm/slub: refactor calculate_order() and calc_slab_order()
>> 
>>  mm/slub.c | 63 ++++++++++++++++++++++++-----------------------------
>> --
>>  1 file changed, 27 insertions(+), 36 deletions(-)
>> 
>