netdev - [PATCH net-next v2] Documentation: add a description for net.core.high_order_alloc

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Message-Id: <20220707080245.180525-1-atenart@kernel.org>
Date:   Thu,  7 Jul 2022 10:02:45 +0200
From:   Antoine Tenart <atenart@...nel.org>
To:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com
Cc:     Antoine Tenart <atenart@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH net-next v2] Documentation: add a description for net.core.high_order_alloc_disable

A description is missing for the net.core.high_order_alloc_disable
option in admin-guide/sysctl/net.rst ; add it. The above sysctl option
was introduced by commit ce27ec60648d ("net: add high_order_alloc_disable
sysctl/static key").

Thanks to Eric for running again the benchmark cited in the above
commit, showing this knob is now mostly of historical importance.

Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Antoine Tenart <atenart@...nel.org>
---

Since v1:
  - Reworked the documentation to mention this knob is now mostly of
    historical importance after Eric ran again the benchmark cited in
    the above commit.

 Documentation/admin-guide/sysctl/net.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index fcd650bdbc7e..805f2281e000 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -391,6 +391,18 @@ 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
 ----------------------------------------------------------
 
-- 
2.36.1