linux-kernel - Re: [RFC PATCH v2 0/3] mm: mempolicy: Multi-tier weighted interleaving

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Message-ID: <ZScQVjDzu0ttYPwC@casper.infradead.org>
Date:   Wed, 11 Oct 2023 22:15:02 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Gregory Price <gourry.memverge@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-cxl@...r.kernel.org, akpm@...ux-foundation.org,
        sthanneeru@...ron.com, ying.huang@...el.com,
        gregory.price@...verge.com
Subject: Re: [RFC PATCH v2 0/3] mm: mempolicy: Multi-tier weighted
 interleaving

On Mon, Oct 09, 2023 at 04:42:56PM -0400, Gregory Price wrote:
> == Mutex to Semaphore change:
> 
> The memory tiering subsystem is extended in this patch set to have
> externally available information (weights), and therefore additional
> controls need to be added to ensure values are not changed (or tiers
> changed/added/removed) during various calculations.
> 
> Since it is expected that many threads will be accessing this data
> during allocations, a mutex is not appropriate.
> 
> Since write-updates (weight changes, hotplug events) are rare events,
> a simple rw semaphore is sufficient.

Given how you're using it, wouldn't the existing RCU mechanism be
better than converting this to an rwsem?