netdev - Re: [PATCH v3 net-next] net: mscc: ocelot: install MAC addresses in .ndo_set_rx

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Date:   Wed, 9 Dec 2020 10:25:43 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        "Allan W . Nielsen" <allan.nielsen@...rochip.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Steen Hegelund <steen.hegelund@...rochip.com>
Subject: Re: [PATCH v3 net-next] net: mscc: ocelot: install MAC addresses in
 .ndo_set_rx_mode from process context

On Wed, 9 Dec 2020 01:56:14 +0000 Vladimir Oltean wrote:
> On Mon, Dec 07, 2020 at 05:09:37PM -0800, Jakub Kicinski wrote:
> > > +	ocelot->owq = alloc_ordered_workqueue("ocelot-owq", WQ_MEM_RECLAIM);  
> >
> > Why MEM_RECLAIM ?  
> 
> Ok, fine, I admit, I copied it.
> 
> After reading the documentation a bit more thoroughly, I am still as
> clear about the guidelines as before. The original logic was, I am
> allocating a memory area and then freeing it from the work item. So it
> must be beneficial for the kernel to want to flush this workqueue during
> the memory reclaim process / under memory pressure, because I am doing
> no memory allocation, and I am also freeing some memory in fact.
> 
> The thing is, there are already a lot of users of WQ_MEM_RECLAIM. Many
> outside of the filesystem/block subsystems. Not sure if all of them
> misuse it, or how to even tell which one constitutes a correct example
> of usage for WQ_MEM_RECLAIM.

Agreed, I wasn't 100% sure either.

I double checked with Tejun, he says it's only needed if the work 
queue is directly used in memory reclaim paths, like writing pages 
out to swap and such.