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Message-ID: <CANn89iKMa5fT3HhKdO2K=WFxwBsRBr_HN=sxPDqX-MJvWyoz5Q@mail.gmail.com>
Date: Thu, 3 Feb 2022 11:54:45 -0800
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Alexander Duyck <alexander.duyck@...il.com>,
Eric Dumazet <eric.dumazet@...il.com>,
"David S . Miller" <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>, Coco Li <lixiaoyan@...gle.com>
Subject: Re: [PATCH net-next 09/15] net: increase MAX_SKB_FRAGS
On Thu, Feb 3, 2022 at 11:20 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> Another issue with CONFIG_ options is that they are integer.
>
> Trying the following did not work
>
> #define MAX_SKB_FRAGS ((unsigned long)CONFIG_MAX_SKB_FRAGS)
>
> Because in some places we have
>
> #if ( MAX_SKB_FRAGS > ...)
>
> (MAX_SKB_FRAGS is UL currently, making it an integer might cause some
> signed/unsigned operations buggy)
I came to something like this, clearly this a bit ugly.
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 08c12c41c5a5907dccc7389f396394d8132d962e..cc3cac3ee109f95c8a51eb90ba4a3bf7bebe86eb
100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -323,7 +323,15 @@ enum skb_drop_reason {
SKB_DROP_REASON_MAX,
};
+#ifdef CONFIG_MAX_SKB_FRAGS_17
+#define MAX_SKB_FRAGS 17UL
+#endif
+#ifdef CONFIG_MAX_SKB_FRAGS_25
+#define MAX_SKB_FRAGS 25UL
+#endif
+#ifdef CONFIG_MAX_SKB_FRAGS_45
#define MAX_SKB_FRAGS 45UL
+#endif
extern int sysctl_max_skb_frags;
diff --git a/net/Kconfig b/net/Kconfig
index 8a1f9d0287de3c32040eee03b60114c6e6d150bc..d91027a654c2aad7bfa55152ef81c882bf394aff
100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -253,6 +253,29 @@ config PCPU_DEV_REFCNT
network device refcount are using per cpu variables if this
option is set.
This can be forced to N to detect underflows (with a
performance drop).
+choice
+ prompt "Maximum number of fragments per skb_shared_info"
+ default MAX_SKB_FRAGS_17
+
+config MAX_SKB_FRAGS_17
+ bool "17 fragments per skb_shared_info"
+ help
+ Some drivers have assumptions about MAX_SKB_FRAGS being 17.
+ Until they are fixed, it is safe to adopt the old limit.
+
+config MAX_SKB_FRAGS_25
+ bool "25 fragments per skb_shared_info"
+ help
+ Helps BIG TCP workloads, but might expose bugs in some legacy drivers.
+
+config MAX_SKB_FRAGS_45
+ bool "45 fragments per skb_shared_info"
+ help
+ Helps BIG TCP workloads, but might expose bugs in some legacy drivers.
+ This also increase memory overhead of small packets.
+
+endchoice
+
config RPS
bool
depends on SMP && SYSFS
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