linux-kernel - Re: [PATCH v2] udmabuf: use kmem

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Message-ID: <36424d42-9d9a-4656-a090-82af9044db8e@vivo.com>
Date: Wed, 31 Jul 2024 15:26:58 +0800
From: Huan Yang <link@...o.com>
To: Gerd Hoffmann <kraxel@...hat.com>, Sumit Semwal
 <sumit.semwal@...aro.org>, Christian König
 <christian.koenig@....com>, dri-devel@...ts.freedesktop.org,
 linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
 linux-kernel@...r.kernel.org
Cc: opensource.kernel@...o.com
Subject: Re: [PATCH v2] udmabuf: use kmem_cache to alloc udmabuf folio


在 2024/7/31 14:26, Huan Yang 写道:
> The current udmabuf_folio contains a list_head and the corresponding
> folio pointer, with a size of 24 bytes. udmabuf_folio uses kmalloc to
> allocate memory.
>
> However, kmalloc is a public pool, starting from 64 bytes. This means
> that each udmabuf_folio allocation will waste 40 bytes.

The description here is incorrect. kmalloc pool is 8 16 32, and so on.

So, each udmabuf_folio(24bytes) use kmalloc will waste 8bytes, not 40.

>
> Considering that each udmabuf creates a folio corresponding to a
> udmabuf_folio, the wasted memory can be significant in the case of
> memory fragmentation.
>
> Furthermore, if udmabuf is frequently used, the allocation and
> deallocation of udmabuf_folio will also be frequent.
>
> Therefore, this patch adds a kmem_cache dedicated to the allocation and
> deallocation of udmabuf_folio.This is expected to improve the
> performance of allocation and deallocation within the expected range,
> while also avoiding memory waste.
>
> Signed-off-by: Huan Yang <link@...o.com>
> ---
> v2 -> v1: fix double unregister, remove unlikely
>
>   drivers/dma-buf/udmabuf.c | 19 +++++++++++++++----
>   1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
> index 047c3cd2ceff..c112c58ef09a 100644
> --- a/drivers/dma-buf/udmabuf.c
> +++ b/drivers/dma-buf/udmabuf.c
> @@ -24,6 +24,8 @@ static int size_limit_mb = 64;
>   module_param(size_limit_mb, int, 0644);
>   MODULE_PARM_DESC(size_limit_mb, "Max size of a dmabuf, in megabytes. Default is 64.");
>   
> +static struct kmem_cache *udmabuf_folio_cachep;
> +
>   struct udmabuf {
>   	pgoff_t pagecount;
>   	struct folio **folios;
> @@ -169,7 +171,7 @@ static void unpin_all_folios(struct list_head *unpin_list)
>   		unpin_folio(ubuf_folio->folio);
>   
>   		list_del(&ubuf_folio->list);
> -		kfree(ubuf_folio);
> +		kmem_cache_free(udmabuf_folio_cachep, ubuf_folio);
>   	}
>   }
>   
> @@ -178,7 +180,7 @@ static int add_to_unpin_list(struct list_head *unpin_list,
>   {
>   	struct udmabuf_folio *ubuf_folio;
>   
> -	ubuf_folio = kzalloc(sizeof(*ubuf_folio), GFP_KERNEL);
> +	ubuf_folio = kmem_cache_alloc(udmabuf_folio_cachep, GFP_KERNEL);
>   	if (!ubuf_folio)
>   		return -ENOMEM;
>   
> @@ -491,11 +493,20 @@ static int __init udmabuf_dev_init(void)
>   					   DMA_BIT_MASK(64));
>   	if (ret < 0) {
>   		pr_err("Could not setup DMA mask for udmabuf device\n");
> -		misc_deregister(&udmabuf_misc);
> -		return ret;
> +		goto err;
> +	}
> +
> +	udmabuf_folio_cachep = KMEM_CACHE(udmabuf_folio, 0);
> +	if (!udmabuf_folio_cachep) {
> +		ret = -ENOMEM;
> +		goto err;
>   	}
>   
>   	return 0;
> +
> +err:
> +	misc_deregister(&udmabuf_misc);
> +	return ret;
>   }
>   
>   static void __exit udmabuf_dev_exit(void)
>
> base-commit: cd19ac2f903276b820f5d0d89de0c896c27036ed