linux-kernel - Re: [PATCH v8] mm/vmalloc: Eliminated the lock contention from twice to once

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Date: Thu, 7 Mar 2024 12:11:13 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: rulinhuang <rulin.huang@...el.com>
Cc: urezki@...il.com, bhe@...hat.com, colin.king@...el.com,
 hch@...radead.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 lstoakes@...il.com, tianyou.li@...el.com, tim.c.chen@...el.com,
 wangyang.guo@...el.com, zhiguo.zhou@...el.com
Subject: Re: [PATCH v8] mm/vmalloc: Eliminated the lock contention from
 twice to once

On Wed,  6 Mar 2024 21:14:40 -0500 rulinhuang <rulin.huang@...el.com> wrote:

> When allocating a new memory area where the mapping address range is
> known, it is observed that the vmap_node->busy.lock is acquired twice.
> 
> The first acquisition occurs in the alloc_vmap_area() function when
> inserting the vm area into the vm mapping red-black tree. The second
> acquisition occurs in the setup_vmalloc_vm() function when updating the
> properties of the vm, such as flags and address, etc.
> 
> Combine these two operations together in alloc_vmap_area(), which
> improves scalability when the vmap_node->busy.lock is contended.
> By doing so, the need to acquire the lock twice can also be eliminated
> to once.
> 
> With the above change, tested on intel sapphire rapids
> platform(224 vcpu), a 4% performance improvement is
> gained on stress-ng/pthread(https://github.com/ColinIanKing/stress-ng),
> which is the stress test of thread creations.
> 

Thanks.  We're late in -rc7 so I'll queue this up for merging in the
next merge window.