linux-kernel - Re: [PATCH v14 084/138] mm/page_alloc: Add folio allocation functions

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Date:   Tue, 10 Aug 2021 22:51:23 +0100
From:   David Howells <dhowells@...hat.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     dhowells@...hat.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v14 084/138] mm/page_alloc: Add folio allocation functions

Matthew Wilcox (Oracle) <willy@...radead.org> wrote:

> +struct folio *folio_alloc(gfp_t gfp, unsigned order)
> +{
> +	struct page *page = alloc_pages(gfp | __GFP_COMP, order);
> +
> +	if (page && order > 1)
> +		prep_transhuge_page(page);

Ummm...  Shouldn't order==1 pages (two page folios) be prep'd also?

> +	return (struct folio *)page;
> +}

Would it be better to just jump to alloc_pages() if order <= 1?  E.g.:

struct folio *folio_alloc(gfp_t gfp, unsigned order)
{
	struct page *page;

	if (order <= 1)
		return (struct folio *)alloc_pages(gfp | __GFP_COMP, order);

	page = alloc_pages(gfp | __GFP_COMP, order);
	if (page)
		prep_transhuge_page(page);
	return (struct folio *)page;
}

David