linux-kernel - Re: [PATCH 1/6] workqueue: Inherit NOIO and NOFS alloc flags

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Date: Mon, 13 May 2024 06:48:38 -1000
From: Tejun Heo <tj@...nel.org>
To: Håkon Bugge <haakon.bugge@...cle.com>
Cc: linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, rds-devel@....oracle.com,
	Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
	Saeed Mahameed <saeedm@...dia.com>,
	Tariq Toukan <tariqt@...dia.com>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Allison Henderson <allison.henderson@...cle.com>,
	Manjunath Patil <manjunath.b.patil@...cle.com>,
	Mark Zhang <markzhang@...dia.com>,
	Chuck Lever <chuck.lever@...cle.com>,
	Shiraz Saleem <shiraz.saleem@...el.com>,
	Yang Li <yang.lee@...ux.alibaba.com>
Subject: Re: [PATCH 1/6] workqueue: Inherit NOIO and NOFS alloc flags

Hello,

On Mon, May 13, 2024 at 02:53:41PM +0200, Håkon Bugge wrote:
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 158784dd189ab..09ecc692ffcae 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -398,6 +398,8 @@ enum wq_flags {
>  	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
>  	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
>  	__WQ_LEGACY		= 1 << 18, /* internal: create*_workqueue() */
> +	__WQ_NOIO               = 1 << 19, /* internal: execute work with NOIO */
> +	__WQ_NOFS               = 1 << 20, /* internal: execute work with NOFS */

I don't quite understand how this is supposed to be used. The flags are
marked internal but nothing actually sets them. Looking at later patches, I
don't see any usages either. What am I missing?

> @@ -3184,6 +3189,12 @@ __acquires(&pool->lock)
>  
>  	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
>  #endif
> +	/* Set inherited alloc flags */
> +	if (use_noio_allocs)
> +		noio_flags = memalloc_noio_save();
> +	if (use_nofs_allocs)
> +		nofs_flags = memalloc_nofs_save();
> +
>  	/* ensure we're on the correct CPU */
>  	WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
>  		     raw_smp_processor_id() != pool->cpu);
> @@ -3320,6 +3331,12 @@ __acquires(&pool->lock)
>  
>  	/* must be the last step, see the function comment */
>  	pwq_dec_nr_in_flight(pwq, work_data);
> +
> +	/* Restore alloc flags */
> +	if (use_nofs_allocs)
> +		memalloc_nofs_restore(nofs_flags);
> +	if (use_noio_allocs)
> +		memalloc_noio_restore(noio_flags);

Also, this looks like something that the work function can do on entry and
before exit, no?

Thanks.

-- 
tejun