linux-kernel - Re: [PATCH net-next v20 06/14] mm: page_frag: reuse existing space for 'size' and 'pfmemalloc'

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Message-ID: <7c4b8aae-dcbd-4d45-b7b0-82609cf8a442@huawei.com>
Date: Fri, 11 Oct 2024 19:40:09 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander Duyck <alexander.duyck@...il.com>
CC: <davem@...emloft.net>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Andrew Morton
	<akpm@...ux-foundation.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH net-next v20 06/14] mm: page_frag: reuse existing space
 for 'size' and 'pfmemalloc'

On 2024/10/10 22:33, Alexander Duyck wrote:

...

> 
> For the decodes yes. I was referring to page_frag_encode_page.
> Basically the output from that isn't anything page frag, it is your
> encoded page type so you could probably just call it
> encoded_page_encode, or encoded_page_create or something like that.

It is kind of confusing as there is some mix of encode/encoded/decode
here, but let's be more specific if it is something like below:

static unsigned long encoded_page_create(struct page *page, unsigned int order,
					 bool pfmemalloc)
{
	BUILD_BUG_ON(PAGE_FRAG_CACHE_MAX_ORDER > PAGE_FRAG_CACHE_ORDER_MASK);
	BUILD_BUG_ON(PAGE_FRAG_CACHE_PFMEMALLOC_BIT >= PAGE_SIZE);

	return (unsigned long)page_address(page) |
		(order & PAGE_FRAG_CACHE_ORDER_MASK) |
		((unsigned long)pfmemalloc * PAGE_FRAG_CACHE_PFMEMALLOC_BIT);
}

static inline bool encoded_page_decode_pfmemalloc(unsigned long encoded_page)
{
	return !!(encoded_page & PAGE_FRAG_CACHE_PFMEMALLOC_BIT);
}

static unsigned long encoded_page_decode_order(unsigned long encoded_page)
{
	return encoded_page & PAGE_FRAG_CACHE_ORDER_MASK;
}

static void *encoded_page_decode_virt(unsigned long encoded_page)
{
	return (void *)(encoded_page & PAGE_MASK);
}

static struct page *encoded_page_decode_page(unsigned long encoded_page)
{
	return virt_to_page((void *)encoded_page);
}