linux-kernel - Re:Re: [PATCH v2] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE

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Message-Id: <1654008072-3136-1-git-send-email-chen45464546@163.com>
Date:   Tue, 31 May 2022 22:41:12 +0800
From:   Chen Lin <chen45464546@....com>
To:     kuba@...nel.org
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, alexander.duyck@...il.com,
        netdev@...r.kernel.org, Chen Lin <chen45464546@....com>
Subject: Re:Re: [PATCH v2] mm: page_frag: Warn_on when frag_alloc size is bigger than PAGE_SIZE

At 2022-05-31 02:29:18, "Jakub Kicinski" <kuba@...nel.org> wrote:
>On Mon, 30 May 2022 12:27:05 -0700 Jakub Kicinski wrote:
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index e008a3df0485..360a545ee5e8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5537,6 +5537,7 @@ EXPORT_SYMBOL(free_pages);
>>   * sk_buff->head, or to be used in the "frags" portion of skb_shared_info.
>>   */
>>  static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
>> +					     unsigned int fragsz,
>>  					     gfp_t gfp_mask)
>>  {
>>  	struct page *page = NULL;
>> @@ -5549,7 +5550,7 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
>>  				PAGE_FRAG_CACHE_MAX_ORDER);
>>  	nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE;
>>  #endif
>> -	if (unlikely(!page))
>> +	if (unlikely(!page && fragsz <= PAGE_SIZE))
>>  		page = alloc_pages_node(NUMA_NO_NODE, gfp, 0);
>>  
>>  	nc->va = page ? page_address(page) : NULL;
>> @@ -5576,7 +5577,7 @@ void *page_frag_alloc_align(struct page_frag_cache *nc,
>>  
>>  	if (unlikely(!nc->va)) {
>>  refill:
>> -		page = __page_frag_cache_refill(nc, gfp_mask);
>> +		page = __page_frag_cache_refill(nc, fragsz, gfp_mask);
>>  		if (!page)
>>  			return NULL;
>
>Oh, well, the reuse also needs an update. We can slap a similar
>condition next to the pfmemalloc check.

The sample code above cannot completely solve the current problem.
For example, when fragsz is greater than PAGE_FRAG_CACHE_MAX_SIZE(32768),
__page_frag_cache_refill will return a memory of only 32768 bytes, so 
should we continue to expand the PAGE_FRAG_CACHE_MAX_SIZE? Maybe more 
work needs to be done