linux-kernel - Re: [PATCH 1/1] mm: vmalloc: Optimize vmap_lazy_nr arithmetic when purging each vmap

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Message-Id: <20240830173338.20c174604ebd8807405a0908@linux-foundation.org>
Date: Fri, 30 Aug 2024 17:33:38 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Adrian Huang <adrianhuang0701@...il.com>
Cc: Uladzislau Rezki <urezki@...il.com>, Christoph Hellwig
 <hch@...radead.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Adrian Huang <ahuang12@...ovo.com>
Subject: Re: [PATCH 1/1] mm: vmalloc: Optimize vmap_lazy_nr arithmetic when
 purging each vmap_area

On Thu, 29 Aug 2024 21:06:33 +0800 Adrian Huang <adrianhuang0701@...il.com> wrote:

> From: Adrian Huang <ahuang12@...ovo.com>
> 
> When running the vmalloc stress on a 448-core system, observe the average
> latency of purge_vmap_node() is about 2 seconds by using the eBPF/bcc
> 'funclatency.py' tool [1].
> 
> ...
>
> 3) The data in column "w/o patch" and "w/ patch"
>      * Unit: micro seconds (us)
>      * Each data is the average of 3-time measurements
> 
>          System        w/o patch (us)   w/ patch (us)    Improvement (%)
>      ---------------   --------------   -------------    -------------
>      72-core server          2194              14            99.36%
>      192-core server       143799            1139            99.21%
>      448-core server      1992122            6883            99.65%
> 

Holy cow.  I'll add cc:stable to this.  Partly because it fixes a
softlockup, partly because holy cow.