linux-kernel - [rfc 6/6] dma-remap: double the default DMA coherent pool size

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Message-ID: <alpine.DEB.2.21.2003011538260.213582@chino.kir.corp.google.com>
Date:   Sun, 1 Mar 2020 16:05:27 -0800 (PST)
From:   David Rientjes <rientjes@...gle.com>
To:     Christoph Hellwig <hch@....de>,
        Tom Lendacky <thomas.lendacky@....com>
cc:     "Singh, Brijesh" <brijesh.singh@....com>,
        "Grimm, Jon" <jon.grimm@....com>, Joerg Roedel <joro@...tes.org>,
        baekhw@...gle.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: [rfc 6/6] dma-remap: double the default DMA coherent pool size

When AMD memory encryption is enabled, some devices may used more than
256KB/sec from the atomic pools.  Double the default size to make the
original size and expansion more appropriate.

This provides a slight optimization on initial expansion and is deemed
appropriate for all configs with CONFIG_DMA_REMAP enabled because of the
increased reliance on the atomic pools.

Alternatively, this could be done only when CONFIG_AMD_MEM_ENCRYPT is
enabled.

Signed-off-by: David Rientjes <rientjes@...gle.com>
---
 kernel/dma/remap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/dma/remap.c b/kernel/dma/remap.c
--- a/kernel/dma/remap.c
+++ b/kernel/dma/remap.c
@@ -105,7 +105,7 @@ static struct gen_pool *atomic_pool __ro_after_init;
 static struct gen_pool *atomic_pool_dma32 __ro_after_init;
 static struct gen_pool *atomic_pool_normal __ro_after_init;
 
-#define DEFAULT_DMA_COHERENT_POOL_SIZE  SZ_256K
+#define DEFAULT_DMA_COHERENT_POOL_SIZE  SZ_512K
 static size_t atomic_pool_size = DEFAULT_DMA_COHERENT_POOL_SIZE;
 
 /* Dynamic background expansion when the atomic pool is near capacity */