linux-kernel - RE: [PATCH v2] dma-debug: Kconfig for PREALLOC_DMA_DEBUG

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Message-ID: <2f2a3bb6b0b9473687628f936db71c4f@AcuMS.aculab.com>
Date:   Tue, 4 Dec 2018 13:36:14 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Qian Cai' <cai@....us>, "hch@....de" <hch@....de>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>
CC:     "yisen.zhuang@...wei.com" <yisen.zhuang@...wei.com>,
        "salil.mehta@...wei.com" <salil.mehta@...wei.com>,
        "john.garry@...wei.com" <john.garry@...wei.com>,
        "linuxarm@...wei.com" <linuxarm@...wei.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] dma-debug: Kconfig for PREALLOC_DMA_DEBUG_ENTRIES

From: Qian Cai
> Sent: 30 November 2018 21:48
> To: hch@....de; m.szyprowski@...sung.com; robin.murphy@....com
> Cc: yisen.zhuang@...wei.com; salil.mehta@...wei.com; john.garry@...wei.com; linuxarm@...wei.com;
> iommu@...ts.linux-foundation.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Qian Cai
> Subject: [PATCH v2] dma-debug: Kconfig for PREALLOC_DMA_DEBUG_ENTRIES
> 
> The amount of DMA mappings from Hisilicon HNS ethernet devices is huge,
> so it could trigger "DMA-API: debugging out of memory - disabling".
> 
> hnae_get_handle [1]
>   hnae_init_queue
>     hnae_init_ring
>       hnae_alloc_buffers [2]
>         debug_dma_map_page
>           dma_entry_alloc
> 
> [1] for (i = 0; i < handle->q_num; i++)
> [2] for (i = 0; i < ring->desc_num; i++)
> 
> Also, "#define HNS_DSAF_MAX_DESC_CNT 1024"
> 
> On this Huawei TaiShan 2280 aarch64 server, it has reached the limit
> already,
> 
> 4 (NICs) x 16 (queues) x 1024 (port descption numbers) = 65536
> 
> Added a Kconfig entry for PREALLOC_DMA_DEBUG_ENTRIES, so make it easier
> for users to deal with special cases like this.

Ugg. That is worse than a module parameter.

The driver needs to automatically reduce the number of mapping requests.

	David

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