linux-kernel - Re: [PATCH v5 7/7] udmabuf: reuse folio array when pin folios

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Message-ID: <90c35051-0528-4dd4-b97b-6ac937b729ab@vivo.com>
Date: Fri, 6 Sep 2024 16:40:32 +0800
From: Huan Yang <link@...o.com>
To: "Kasireddy, Vivek" <vivek.kasireddy@...el.com>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 Gerd Hoffmann <kraxel@...hat.com>,
 "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: "opensource.kernel@...o.com" <opensource.kernel@...o.com>
Subject: Re: [PATCH v5 7/7] udmabuf: reuse folio array when pin folios


在 2024/9/6 16:23, Kasireddy, Vivek 写道:
> Hi Huan,
>
>> Subject: [PATCH v5 7/7] udmabuf: reuse folio array when pin folios
>>
>> When invoke memfd_pin_folios, we need offer an array to save each folio
>> which we pinned.
>>
>> The currently way is dynamic alloc an array, get folios, save into
>> udmabuf and then free.
>>
>> If the size is tiny, alloc from slab, is ok due to slab can cache it.
>> Or, just PCP order can cover, also ok.
>>
>> But if size is huge, need fallback into vmalloc, then, not well, due to
>> each page will iter alloc, and map into vmalloc area. Too heavy.
>>
>> Now that we need to iter each udmabuf item, then pin it's range folios,
>> we can reuse the maximum size range's folios array.
>>
>> Signed-off-by: Huan Yang <link@...o.com>
>> ---
>>   drivers/dma-buf/udmabuf.c | 34 ++++++++++++++++++++--------------
>>   1 file changed, 20 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
>> index d449c1fd67a5..d70e45c33442 100644
>> --- a/drivers/dma-buf/udmabuf.c
>> +++ b/drivers/dma-buf/udmabuf.c
>> @@ -343,28 +343,21 @@ static int export_udmabuf(struct udmabuf *ubuf,
>>   }
>>
>>   static int udmabuf_pin_folios(struct udmabuf *ubuf, struct file *memfd,
>> -			      loff_t start, loff_t size)
>> +			      loff_t start, loff_t size, struct folio **folios)
>>   {
>>   	pgoff_t pgoff, pgcnt;
>>   	pgoff_t upgcnt = ubuf->pagecount;
>>   	pgoff_t nr_pinned = ubuf->nr_pinned;
>>   	u32 cur_folio, cur_pgcnt;
>> -	struct folio **folios = NULL;
>>   	long nr_folios;
>>   	loff_t end;
>>   	int ret = 0;
>>
>>   	pgcnt = size >> PAGE_SHIFT;
>> -	folios = kvmalloc_array(pgcnt, sizeof(*folios), GFP_KERNEL);
>> -	if (!folios)
>> -		return -ENOMEM;
>> -
>>   	end = start + (pgcnt << PAGE_SHIFT) - 1;
>>   	nr_folios = memfd_pin_folios(memfd, start, end, folios, pgcnt,
>> &pgoff);
>> -	if (nr_folios <= 0) {
>> -		ret = nr_folios ? nr_folios : -EINVAL;
>> -		goto err;
>> -	}
>> +	if (nr_folios <= 0)
>> +		return nr_folios ? nr_folios : -EINVAL;
>>
>>   	cur_pgcnt = 0;
>>   	for (cur_folio = 0; cur_folio < nr_folios; ++cur_folio) {
>> @@ -389,10 +382,8 @@ static int udmabuf_pin_folios(struct udmabuf
>> *ubuf, struct file *memfd,
>>   		pgoff = 0;
>>   	}
>>   end:
>> -err:
>>   	ubuf->pagecount = upgcnt;
>>   	ubuf->nr_pinned = nr_pinned;
>> -	kvfree(folios);
>>   	return ret;
> The variable ret is now unused in this function. Remove it and just
> return 0 at the end.

Oh, nice catch.

Thanks.

>
>>   }
>>
>> @@ -403,6 +394,8 @@ static long udmabuf_create(struct miscdevice
>> *device,
>>   	pgoff_t pgcnt = 0, pglimit;
>>   	long ret = -EINVAL;
>>   	struct udmabuf *ubuf;
>> +	struct folio **folios = NULL;
>> +	unsigned long max_nr_folios = 0;
>>   	u32 i, flags;
>>
>>   	ubuf = kzalloc(sizeof(*ubuf), GFP_KERNEL);
>> @@ -411,14 +404,19 @@ static long udmabuf_create(struct miscdevice
>> *device,
>>
>>   	pglimit = (size_limit_mb * 1024 * 1024) >> PAGE_SHIFT;
>>   	for (i = 0; i < head->count; i++) {
>> +		pgoff_t subpgcnt;
>> +
>>   		if (!PAGE_ALIGNED(list[i].offset))
>>   			goto err_noinit;
>>   		if (!PAGE_ALIGNED(list[i].size))
>>   			goto err_noinit;
>>
>> -		pgcnt += list[i].size >> PAGE_SHIFT;
>> +		subpgcnt = list[i].size >> PAGE_SHIFT;
>> +		pgcnt += subpgcnt;
>>   		if (pgcnt > pglimit)
>>   			goto err_noinit;
>> +
>> +		max_nr_folios = max_t(unsigned long, subpgcnt,
>> max_nr_folios);
>>   	}
>>
>>   	if (!pgcnt)
>> @@ -428,6 +426,12 @@ static long udmabuf_create(struct miscdevice
>> *device,
>>   	if (ret)
>>   		goto err;
>>
>> +	folios = kvmalloc_array(max_nr_folios, sizeof(*folios), GFP_KERNEL);
>> +	if (!folios) {
>> +		ret = -ENOMEM;
>> +		goto err;
>> +	}
>> +
>>   	for (i = 0; i < head->count; i++) {
>>   		struct file *memfd = fget(list[i].memfd);
>>
>> @@ -436,7 +440,7 @@ static long udmabuf_create(struct miscdevice
>> *device,
>>   			goto err;
>>
>>   		ret = udmabuf_pin_folios(ubuf, memfd, list[i].offset,
>> -					 list[i].size);
>> +					 list[i].size, folios);
>>   		fput(memfd);
>>   		if (ret)
>>   			goto err;
>> @@ -447,12 +451,14 @@ static long udmabuf_create(struct miscdevice
>> *device,
>>   	if (ret < 0)
>>   		goto err;
>>
>> +	kvfree(folios);
> Acked-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
>
>>   	return ret;
>>
>>   err:
>>   	deinit_udmabuf(ubuf);
>>   err_noinit:
>>   	kfree(ubuf);
>> +	kvfree(folios);
>>   	return ret;
>>   }
>>
>> --
>> 2.45.2