linux-kernel - Re: [PATCH v3] udmabuf: use kmem

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Message-ID: <50a3b561-5946-45b2-954e-ea95050ba459@vivo.com>
Date: Thu, 1 Aug 2024 09:39:30 +0800
From: Huan Yang <link@...o.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>,
 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 v3] udmabuf: use kmem_cache to alloc udmabuf folio


在 2024/8/1 1:11, Christophe JAILLET 写道:
> [Some people who received this message don't often get email from 
> christophe.jaillet@...adoo.fr. Learn why this is important at 
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>
> Le 31/07/2024 à 09:37, Huan Yang a écrit :
>> 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 8,16,32 bytes.
>> Additionally, if the size is not aligned with the kmalloc size, it will
>> be rounded up to the corresponding size.
>> This means that each udmabuf_folio allocation will get 32 bytes, and
>> waste 8 bytes.
>>
>> 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>
>> ---
>> v3 -> v2: fix error description.
>> 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)
>
> Hi,
>
> should a kmem_cache_destroy() be also added in udmabuf_dev_exit()?
Yes, thanks for point this.
>
> CJ
>
>>
>> base-commit: cd19ac2f903276b820f5d0d89de0c896c27036ed
>