[RFC PATCH] mm: net: disable kswapd for high-order network buffer allocation

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

On phones, we have observed significant phone heating when running apps
with high network bandwidth. This is caused by the network stack frequently
waking kswapd for order-3 allocations. As a result, memory reclamation becomes
constantly active, even though plenty of memory is still available for network
allocations which can fall back to order-0.

Commit ce27ec60648d ("net: add high_order_alloc_disable sysctl/static key")
introduced high_order_alloc_disable for the transmit (TX) path
(skb_page_frag_refill()) to mitigate some memory reclamation issues,
allowing the TX path to fall back to order-0 immediately, while leaving the
receive (RX) path (__page_frag_cache_refill()) unaffected. Users are
generally unaware of the sysctl and cannot easily adjust it for specific use
cases. Enabling high_order_alloc_disable also completely disables the
benefit of order-3 allocations. Additionally, the sysctl does not apply to the
RX path.

An alternative approach is to disable kswapd for these frequent
allocations and provide best-effort order-3 service for both TX and RX paths,
while removing the sysctl entirely.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Kuniyuki Iwashima <kuniyu@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Simon Horman <horms@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Huacai Zhou <zhouhuacai@oppo.com>
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 Documentation/admin-guide/sysctl/net.rst | 12 ------------
 include/net/sock.h                       |  1 -
 mm/page_frag_cache.c                     |  2 +-
 net/core/sock.c                          |  8 ++------
 net/core/sysctl_net_core.c               |  7 -------
 5 files changed, 3 insertions(+), 27 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index 2ef50828aff1..b903bbae239c 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -415,18 +415,6 @@ GRO has decided not to coalesce, it is placed on a per-NAPI list. This
 list is then passed to the stack when the number of segments reaches the
 gro_normal_batch limit.
 
-high_order_alloc_disable
-------------------------
-
-By default the allocator for page frags tries to use high order pages (order-3
-on x86). While the default behavior gives good results in most cases, some users
-might have hit a contention in page allocations/freeing. This was especially
-true on older kernels (< 5.14) when high-order pages were not stored on per-cpu
-lists. This allows to opt-in for order-0 allocation instead but is now mostly of
-historical importance.
-
-Default: 0
-
 2. /proc/sys/net/unix - Parameters for Unix domain sockets
 ----------------------------------------------------------
 
diff --git a/include/net/sock.h b/include/net/sock.h
index 60bcb13f045c..62306c1095d5 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -3011,7 +3011,6 @@ extern __u32 sysctl_wmem_default;
 extern __u32 sysctl_rmem_default;
 
 #define SKB_FRAG_PAGE_ORDER	get_order(32768)
-DECLARE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
 
 static inline int sk_get_wmem0(const struct sock *sk, const struct proto *proto)
 {
diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c
index d2423f30577e..dd36114dd16f 100644
--- a/mm/page_frag_cache.c
+++ b/mm/page_frag_cache.c
@@ -54,7 +54,7 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
 	gfp_t gfp = gfp_mask;
 
 #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
-	gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |  __GFP_COMP |
+	gfp_mask = (gfp_mask & ~__GFP_RECLAIM) |  __GFP_COMP |
 		   __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
 	page = __alloc_pages(gfp_mask, PAGE_FRAG_CACHE_MAX_ORDER,
 			     numa_mem_id(), NULL);
diff --git a/net/core/sock.c b/net/core/sock.c
index dc03d4b5909a..1fa1e9177d86 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3085,8 +3085,6 @@ static void sk_leave_memory_pressure(struct sock *sk)
 	}
 }
 
-DEFINE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
-
 /**
  * skb_page_frag_refill - check that a page_frag contains enough room
  * @sz: minimum size of the fragment we want to get
@@ -3110,10 +3108,8 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
 	}
 
 	pfrag->offset = 0;
-	if (SKB_FRAG_PAGE_ORDER &&
-	    !static_branch_unlikely(&net_high_order_alloc_disable_key)) {
-		/* Avoid direct reclaim but allow kswapd to wake */
-		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
+	if (SKB_FRAG_PAGE_ORDER) {
+		pfrag->page = alloc_pages((gfp & ~__GFP_RECLAIM) |
 					  __GFP_COMP | __GFP_NOWARN |
 					  __GFP_NORETRY,
 					  SKB_FRAG_PAGE_ORDER);
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 8cf04b57ade1..181f6532beb8 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -599,13 +599,6 @@ static struct ctl_table net_core_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_THREE,
 	},
-	{
-		.procname	= "high_order_alloc_disable",
-		.data		= &net_high_order_alloc_disable_key.key,
-		.maxlen         = sizeof(net_high_order_alloc_disable_key),
-		.mode		= 0644,
-		.proc_handler	= proc_do_static_key,
-	},
 	{
 		.procname	= "gro_normal_batch",
 		.data		= &net_hotdata.gro_normal_batch,
-- 
2.39.3 (Apple Git-146)