linux-kernel - Re: [PATCH v5 0/7] mm, slab: Make kmalloc

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Message-ID: <0100016d3ad11d18-fb812791-af73-43aa-b430-ba1889f1a85c-000000@email.amazonses.com>
Date:   Mon, 16 Sep 2019 16:04:06 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Pengfei Li <lpf.vector@...il.com>
cc:     akpm@...ux-foundation.org, vbabka@...e.cz, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, guro@...com
Subject: Re: [PATCH v5 0/7] mm, slab: Make kmalloc_info[] contain all types
 of names

On Mon, 16 Sep 2019, Pengfei Li wrote:

> The name of KMALLOC_NORMAL is contained in kmalloc_info[].name,
> but the names of KMALLOC_RECLAIM and KMALLOC_DMA are dynamically
> generated by kmalloc_cache_name().
>
> Patch1 predefines the names of all types of kmalloc to save
> the time spent dynamically generating names.
>
> These changes make sense, and the time spent by new_kmalloc_cache()
> has been reduced by approximately 36.3%.

This is time spend during boot and does not affect later system
performance.

>                          Time spent by new_kmalloc_cache()
>                                   (CPU cycles)
> 5.3-rc7                              66264
> 5.3-rc7+patch_1-3                    42188

Ok. 15k cycles during boot saved. So we save 5 microseconds during bootup?

The current approach was created with the view on future setups allowing a
dynamic configuration of kmalloc caches based on need. I.e. ZONE_DMA may
not be needed once the floppy driver no longer makes use of it.