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

Ryan Roberts
2024-10-16T14:50:15Z

+ 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,