Re: [RFC PATCH v1 23/57] net: Remove PAGE_SIZE compile-time constant assumption

[Ryan Roberts <ryan.roberts@arm.com>]

+ Chuck Lever, Jeff Layton

This was a rather tricky series to get the recipients correct for and my script
did not realize that "supporter" was a pseudonym for "maintainer" so you were
missed off the original post. Appologies!

More context in cover letter:
https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/


On 14/10/2024 11:58, Ryan Roberts wrote:
> To prepare for supporting boot-time page size selection, refactor code
> to remove assumptions about PAGE_SIZE being compile-time constant. Code
> intended to be equivalent when compile-time page size is active.
> 
> Define NLMSG_GOODSIZE using min() instead of ifdeffery. This will now
> evaluate to a compile-time constant for compile-time page size, but
> evaluate at run-time when using boot-time page size.
> 
> Rework NAPI small page frag infrastructure so that for boot-time page
> size it is compiled in if 4K page size is in the possible range, but
> defer deciding to use it to run time when the page size is known. No
> change for compile-time page size case.
> 
> Resize cache_defer_hash[] array for PAGE_SIZE_MAX.
> 
> Convert a complex BUILD_BUG_ON() to runtime BUG_ON().
> 
> Wrap global variables that are initialized with PAGE_SIZE derived values
> using DEFINE_GLOBAL_PAGE_SIZE_VAR() so their initialization can be
> deferred for boot-time page size builds.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
> 
> ***NOTE***
> Any confused maintainers may want to read the cover note here for context:
> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
> 
>  include/linux/netlink.h    | 6 +-----
>  net/core/hotdata.c         | 4 ++--
>  net/core/skbuff.c          | 4 ++--
>  net/core/sysctl_net_core.c | 2 +-
>  net/sunrpc/cache.c         | 3 ++-
>  net/unix/af_unix.c         | 2 +-
>  6 files changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> index b332c2048c755..ffa1e94111f89 100644
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -267,11 +267,7 @@ netlink_skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
>   *	use enormous buffer sizes on recvmsg() calls just to avoid
>   *	MSG_TRUNC when PAGE_SIZE is very large.
>   */
> -#if PAGE_SIZE < 8192UL
> -#define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(PAGE_SIZE)
> -#else
> -#define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(8192UL)
> -#endif
> +#define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(min(PAGE_SIZE, 8192UL))
>  
>  #define NLMSG_DEFAULT_SIZE (NLMSG_GOODSIZE - NLMSG_HDRLEN)
>  
> diff --git a/net/core/hotdata.c b/net/core/hotdata.c
> index d0aaaaa556f22..e1f30e87ba6e9 100644
> --- a/net/core/hotdata.c
> +++ b/net/core/hotdata.c
> @@ -5,7 +5,7 @@
>  #include <net/hotdata.h>
>  #include <net/proto_memory.h>
>  
> -struct net_hotdata net_hotdata __cacheline_aligned = {
> +__DEFINE_GLOBAL_PAGE_SIZE_VAR(struct net_hotdata, net_hotdata, __cacheline_aligned, {
>  	.offload_base = LIST_HEAD_INIT(net_hotdata.offload_base),
>  	.ptype_all = LIST_HEAD_INIT(net_hotdata.ptype_all),
>  	.gro_normal_batch = 8,
> @@ -21,5 +21,5 @@ struct net_hotdata net_hotdata __cacheline_aligned = {
>  	.sysctl_max_skb_frags = MAX_SKB_FRAGS,
>  	.sysctl_skb_defer_max = 64,
>  	.sysctl_mem_pcpu_rsv = SK_MEMORY_PCPU_RESERVE
> -};
> +});
>  EXPORT_SYMBOL(net_hotdata);
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 83f8cd8aa2d16..b6c8eee0cc74b 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -219,9 +219,9 @@ static void skb_under_panic(struct sk_buff *skb, unsigned int sz, void *addr)
>  #define NAPI_SKB_CACHE_BULK	16
>  #define NAPI_SKB_CACHE_HALF	(NAPI_SKB_CACHE_SIZE / 2)
>  
> -#if PAGE_SIZE == SZ_4K
> +#if PAGE_SIZE_MIN <= SZ_4K && SZ_4K <= PAGE_SIZE_MAX
>  
> -#define NAPI_HAS_SMALL_PAGE_FRAG	1
> +#define NAPI_HAS_SMALL_PAGE_FRAG	(PAGE_SIZE == SZ_4K)
>  #define NAPI_SMALL_PAGE_PFMEMALLOC(nc)	((nc).pfmemalloc)
>  
>  /* specialized page frag allocator using a single order 0 page
> diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
> index 86a2476678c48..a7a2eb7581bd1 100644
> --- a/net/core/sysctl_net_core.c
> +++ b/net/core/sysctl_net_core.c
> @@ -33,7 +33,7 @@ static int int_3600 = 3600;
>  static int min_sndbuf = SOCK_MIN_SNDBUF;
>  static int min_rcvbuf = SOCK_MIN_RCVBUF;
>  static int max_skb_frags = MAX_SKB_FRAGS;
> -static int min_mem_pcpu_rsv = SK_MEMORY_PCPU_RESERVE;
> +static DEFINE_GLOBAL_PAGE_SIZE_VAR(int, min_mem_pcpu_rsv, SK_MEMORY_PCPU_RESERVE);
>  
>  static int net_msg_warn;	/* Unused, but still a sysctl */
>  
> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
> index 95ff747061046..4e682c0cd7586 100644
> --- a/net/sunrpc/cache.c
> +++ b/net/sunrpc/cache.c
> @@ -573,13 +573,14 @@ EXPORT_SYMBOL_GPL(cache_purge);
>   */
>  
>  #define	DFR_HASHSIZE	(PAGE_SIZE/sizeof(struct list_head))
> +#define	DFR_HASHSIZE_MAX (PAGE_SIZE_MAX/sizeof(struct list_head))
>  #define	DFR_HASH(item)	((((long)item)>>4 ^ (((long)item)>>13)) % DFR_HASHSIZE)
>  
>  #define	DFR_MAX	300	/* ??? */
>  
>  static DEFINE_SPINLOCK(cache_defer_lock);
>  static LIST_HEAD(cache_defer_list);
> -static struct hlist_head cache_defer_hash[DFR_HASHSIZE];
> +static struct hlist_head cache_defer_hash[DFR_HASHSIZE_MAX];
>  static int cache_defer_cnt;
>  
>  static void __unhash_deferred_req(struct cache_deferred_req *dreq)
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 0be0dcb07f7b6..1cf9f583358af 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -2024,7 +2024,7 @@ static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
>  				 MAX_SKB_FRAGS * PAGE_SIZE);
>  		data_len = PAGE_ALIGN(data_len);
>  
> -		BUILD_BUG_ON(SKB_MAX_ALLOC < PAGE_SIZE);
> +		BUG_ON(SKB_MAX_ALLOC < PAGE_SIZE);
>  	}
>  
>  	skb = sock_alloc_send_pskb(sk, len - data_len, data_len,