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: <CAKgT0UdavkCTqvNUZt6JmKK5NrMQmDbNi+S1LLrZeYfp3Ofn5w@mail.gmail.com>
Date: Fri, 11 Oct 2024 08:31:49 -0700
From: Alexander Duyck <alexander.duyck@...il.com>
To: Yunsheng Lin <linyunsheng@...wei.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 Fri, Oct 11, 2024 at 4:40 AM Yunsheng Lin <linyunsheng@...wei.com> wrote:
>
> 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);
> }

Yes, this is what I had in mind. Basically the encoded_page is the
object you are working on so it becomes the prefix for the function
name and the action is the suffix, so you are either doing a "create"
to put together the object, or performing a "decode" to get the
individual components.