Re: [PATCH resend] mm: hugetlb_vmemmap: use bulk allocator in alloc_vmemmap_page_list()

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> On Sep 6, 2023, at 11:13, Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
> 
> 
> 
> On 2023/9/6 10:47, Matthew Wilcox wrote:
>> On Tue, Sep 05, 2023 at 06:35:08PM +0800, Kefeng Wang wrote:
>>> It is needed 4095 pages(1G) or 7 pages(2M) to be allocated once in
>>> alloc_vmemmap_page_list(), so let's add a bulk allocator varietas
>>> alloc_pages_bulk_list_node() and switch alloc_vmemmap_page_list()
>>> to use it to accelerate page allocation.
>> Argh, no, please don't do this.
>> Iterating a linked list is _expensive_.  It is about 10x quicker to
>> iterate an array than a linked list.  Adding the list_head option
>> to __alloc_pages_bulk() was a colossal mistake.  Don't perpetuate it.
>> These pages are going into an array anyway.  Don't put them on a list
>> first.
> 
> struct vmemmap_remap_walk - walk vmemmap page table
> 
> * @vmemmap_pages:  the list head of the vmemmap pages that can be freed
> *                  or is mapped from.
> 
> At present, the struct vmemmap_remap_walk use a list for vmemmap page table walk, so do you mean we need change vmemmap_pages from a list to a array firstly and then use array bulk api, even kill list bulk api ?

It'll be a little complex for hugetlb_vmemmap. Should it be reasonable to
directly use __alloc_pages_bulk in hugetlb_vmemmap itself?






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