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Subject: Re: [PATCH] mm/vmalloc: add missing __GFP_HIGHMEM flag for vmalloc
To:     Matthew Wilcox <willy@infradead.org>
CC:     <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <wangkefeng.wang@huawei.com>,
        <weiyongjun1@huawei.com>
References: <20210726032333.3404164-1-chenwandun@huawei.com>
 <YP4rM7qtSet+H+nG@casper.infradead.org>
From:   Chen Wandun <chenwandun@huawei.com>
Message-ID: <f064b046-8831-2aa9-2234-63e867e28dc1@huawei.com>
Date:   Mon, 26 Jul 2021 12:05:44 +0800
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在 2021/7/26 11:25, Matthew Wilcox 写道:
> On Mon, Jul 26, 2021 at 11:23:33AM +0800, Chen Wandun wrote:
>> struct page array can also be allocated in highmem during vmalloc,
>> that will ease the low memory stress in 32bit system.
> Huh?  Where does it get kmapped in order to access it?

The struct page array contain numbers of pointer of struct page, it is used to save

pages that allocated for vmalloc mapping in vmap_pages_range, it does't need to kmap.


The main idea of this patch is come from:

https://lore.kernel.org/lkml/20170307141020.29107-1-mhocko@kernel.org/

>
>> Fixes: f255935b9767 ("mm: cleanup the gfp_mask handling in __vmalloc_area_node")
>> Signed-off-by: Chen Wandun <chenwandun@huawei.com>
>> ---
>>   mm/vmalloc.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 3824dc16ce1c..8d9b0b08a6dc 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -2885,7 +2885,8 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>>   
>>   	/* Please note that the recursion is strictly bounded. */
>>   	if (array_size > PAGE_SIZE) {
>> -		area->pages = __vmalloc_node(array_size, 1, nested_gfp, node,
>> +		area->pages = __vmalloc_node(array_size, 1,
>> +					nested_gfp | __GFP_HIGHMEM, node,
>>   					area->caller);
>>   	} else {
>>   		area->pages = kmalloc_node(array_size, nested_gfp, node);
>> -- 
>> 2.25.1
>>
>>
> .