linux-kernel - Re: [PATCH v5 3/4] apparmor: experiment with faster backoff on global buffer

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Message-ID: <acc4a7fa-d423-418d-81d7-35d4416afdd0@canonical.com>
Date:   Tue, 17 Oct 2023 02:25:23 -0700
From:   John Johansen <john.johansen@...onical.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Anil Altinay <aaltinay@...gle.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        LKLM <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Tomasz Figa <tfiga@...omium.org>,
        linux-security-module@...r.kernel.org,
        John Johansen <john.johansen@...onical.com>
Subject: Re: [PATCH v5 3/4] apparmor: experiment with faster backoff on global
 buffer

Instead of doubling hold count when contention is encounter increase
it by 8x. This makes for a faster back off, but results in buffers
being held longer.

Signed-off-by: John Johansen <john.johansen@...onical.com>
---
  security/apparmor/lsm.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index fd6779ff0da4..52423d88854a 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1796,10 +1796,10 @@ static int param_set_mode(const char *val, const struct kernel_param *kp)
  
  static void update_contention(struct aa_local_cache *cache)
  {
-	cache->contention += 1;
+	cache->contention += 3;
  	if (cache->contention > 9)
  		cache->contention = 9;
-	cache->hold += 1 << cache->contention;		/* 2, 4, 8, ... */
+	cache->hold += 1 << cache->contention;		/* 8, 64, 512, ... */
  }
  
  char *aa_get_buffer(bool in_atomic)
-- 
2.34.1