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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

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 ?