linux-kernel - Re: [PATCH v6 1/3] dmapool: add NUMA affinity support

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Message-ID: <aA-YS8Bv0kO75jdk@kbusch-mbp.dhcp.thefacebook.com>
Date: Mon, 28 Apr 2025 09:01:31 -0600
From: Keith Busch <kbusch@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: Caleb Sander Mateos <csander@...estorage.com>,
	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kanchan Joshi <joshi.k@...sung.com>, linux-nvme@...ts.infradead.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/3] dmapool: add NUMA affinity support

On Mon, Apr 28, 2025 at 11:35:12AM +0100, John Garry wrote:
> >   static struct dma_page *pool_alloc_page(struct dma_pool *pool, gfp_t mem_flags)
> >   {
> >   	struct dma_page *page;
> > -	page = kmalloc(sizeof(*page), mem_flags);
> > +	page = kmalloc_node(sizeof(*page), mem_flags, pool->node);
> >   	if (!page)
> >   		return NULL;
> 
> For pool->node != NUMA_NO_NODE, pool->node == numa_node_id(), right? I
> mean, aren't we on a CPU in pool->node here?

Not necessarily. blk-mq hctx's could span numa nodes. We just want to
register the dma pool with whichever one is the first node.