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

[Matthew Wilcox <willy@infradead.org>]

On Wed, Sep 06, 2023 at 11:13:27AM +0800, Kefeng Wang 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 ?

That would be better, yes.