Re: [PATCH 1/4] pagevec: Allow pagevecs to be different sizes

[Kent Overstreet <kent.overstreet@gmail.com>]

On Fri, Nov 06, 2020 at 12:30:37PM +0000, Matthew Wilcox (Oracle) wrote:
> Declaring a pagevec continues to create a pagevec which is the same size,
> but functions which manipulate pagevecs no longer rely on this.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  include/linux/pagevec.h | 20 ++++++++++++++++----
>  mm/swap.c               |  8 ++++++++
>  2 files changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
> index 875a3f0d9dd2..ee5d3c4da8da 100644
> --- a/include/linux/pagevec.h
> +++ b/include/linux/pagevec.h
> @@ -18,9 +18,15 @@ struct page;
>  struct address_space;
>  
>  struct pagevec {
> -	unsigned char nr;
> -	bool percpu_pvec_drained;
> -	struct page *pages[PAGEVEC_SIZE];
> +	union {
> +		struct {
> +			unsigned char sz;
> +			unsigned char nr;
> +			bool percpu_pvec_drained;
This should probably be removed, it's only used by the swap code and I don't
think it belongs in the generic data structure. That would mean nr and size (and
let's please use more standard naming...) can be u32, not u8s.

> +			struct page *pages[PAGEVEC_SIZE];
> +		};
> +		void *__p[PAGEVEC_SIZE + 1];

What's up with this union?

> +	};
>  };
>  
>  void __pagevec_release(struct pagevec *pvec);
> @@ -41,6 +47,7 @@ static inline unsigned pagevec_lookup_tag(struct pagevec *pvec,
>  
>  static inline void pagevec_init(struct pagevec *pvec)
>  {
> +	pvec->sz = PAGEVEC_SIZE;
>  	pvec->nr = 0;
>  	pvec->percpu_pvec_drained = false;
>  }
> @@ -50,6 +57,11 @@ static inline void pagevec_reinit(struct pagevec *pvec)
>  	pvec->nr = 0;
>  }
>  
> +static inline unsigned pagevec_size(struct pagevec *pvec)
> +{
> +	return pvec->sz;
> +}
> +
>  static inline unsigned pagevec_count(struct pagevec *pvec)
>  {
>  	return pvec->nr;
> @@ -57,7 +69,7 @@ static inline unsigned pagevec_count(struct pagevec *pvec)
>  
>  static inline unsigned pagevec_space(struct pagevec *pvec)
>  {
> -	return PAGEVEC_SIZE - pvec->nr;
> +	return pvec->sz - pvec->nr;
>  }
>  
>  /*
> diff --git a/mm/swap.c b/mm/swap.c
> index 2ee3522a7170..d093fb30f038 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -52,6 +52,7 @@ struct lru_rotate {
>  };
>  static DEFINE_PER_CPU(struct lru_rotate, lru_rotate) = {
>  	.lock = INIT_LOCAL_LOCK(lock),
> +	.pvec.sz = PAGEVEC_SIZE,
>  };
>  
>  /*
> @@ -70,6 +71,13 @@ struct lru_pvecs {
>  };
>  static DEFINE_PER_CPU(struct lru_pvecs, lru_pvecs) = {
>  	.lock = INIT_LOCAL_LOCK(lock),
> +	.lru_add.sz = PAGEVEC_SIZE,
> +	.lru_deactivate_file.sz = PAGEVEC_SIZE,
> +	.lru_deactivate.sz = PAGEVEC_SIZE,
> +	.lru_lazyfree.sz = PAGEVEC_SIZE,
> +#ifdef CONFIG_SMP
> +	.activate_page.sz = PAGEVEC_SIZE,
> +#endif
>  };
>  
>  /*
> -- 
> 2.28.0
>