linux-kernel - [PATCH] dma-debug: increase HASH

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Message-Id: <20191030184844.84219-1-edumazet@google.com>
Date:   Wed, 30 Oct 2019 11:48:44 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: [PATCH] dma-debug: increase HASH_SIZE

With modern NIC, it is not unusual having about ~256,000 active dma
mappings. Hash size of 1024 buckets is too small.

Forcing full cache line per bucket does not seem useful,
especially now that we have a contention on free_entries_lock
for allocations and freeing of entries. Better using space
to fit more buckets.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Christoph Hellwig <hch@....de>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>
---
 kernel/dma/debug.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 4ad74f5987ea9e95f9bb5e2d1592254e367d24fb..35e2a853bff9c482d789ab331d79aaee07753a97 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -27,7 +27,7 @@
 
 #include <asm/sections.h>
 
-#define HASH_SIZE       1024ULL
+#define HASH_SIZE       16384ULL
 #define HASH_FN_SHIFT   13
 #define HASH_FN_MASK    (HASH_SIZE - 1)
 
@@ -87,7 +87,7 @@ typedef bool (*match_fn)(struct dma_debug_entry *, struct dma_debug_entry *);
 struct hash_bucket {
 	struct list_head list;
 	spinlock_t lock;
-} ____cacheline_aligned_in_smp;
+};
 
 /* Hash list to save the allocated dma addresses */
 static struct hash_bucket dma_entry_hash[HASH_SIZE];
-- 
2.24.0.rc0.303.g954a862665-goog