linux-kernel - Re: [PATCH 04/28] dma-mapping: use vmap insted of reimplementing it

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Message-ID: <20200408154225.GA28676@lst.de>
Date:   Wed, 8 Apr 2020 17:42:25 +0200
From:   Christoph Hellwig <hch@....de>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/28] dma-mapping: use vmap insted of reimplementing it

On Wed, Apr 08, 2020 at 09:17:36PM +0800, Hillf Danton wrote:
> > @@ -62,24 +42,20 @@ void *dma_common_pages_remap(struct page **pages, size_t size,
> >  void *dma_common_contiguous_remap(struct page *page, size_t size,
> >  			pgprot_t prot, const void *caller)
> >  {
> > -	int i;
> > +	int count = size >> PAGE_SHIFT;
> >  	struct page **pages;
> > -	struct vm_struct *area;
> > +	void *vaddr;
> > +	int i;
> >  
> > -	pages = kmalloc(sizeof(struct page *) << get_order(size), GFP_KERNEL);
> > +	pages = kmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
> 
> Is it making sense to vmalloc pages as long as array size is bigger than
> PAGE_SIZE?

Maybe, maybe not.  But it certainly doesn't fit this series.