Re: [PATCH 08/12] hugetlb: batch freeing of vmemmap pages

[Mike Kravetz <mike.kravetz@oracle.com>]

On 08/30/23 15:20, Muchun Song wrote:
> 
> 
> On 2023/8/26 03:04, Mike Kravetz wrote:
> > Now that batching of hugetlb vmemmap optimization processing is possible,
> > batch the freeing of vmemmap pages.  When freeing vmemmap pages for a
> > hugetlb page, we add them to a list that is freed after the entire batch
> > has been processed.
> > 
> > This enhances the ability to return contiguous ranges of memory to the
> > low level allocators.
> > 
> > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> > ---
> >   mm/hugetlb_vmemmap.c | 56 ++++++++++++++++++++++++++++++++------------
> >   1 file changed, 41 insertions(+), 15 deletions(-)
> > 
> > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> > index d5e6b6c76dce..e390170c0887 100644
> > --- a/mm/hugetlb_vmemmap.c
> > +++ b/mm/hugetlb_vmemmap.c
> > @@ -305,11 +305,14 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
> >    * @end:	end address of the vmemmap virtual address range that we want to
> >    *		remap.
> >    * @reuse:	reuse address.
> > + * @bulk_pages: list to deposit vmemmap pages to be freed in bulk operations
> > + *		or NULL in non-bulk case;
> 
> I'd like to rename bulk_pages to vmemmap_pages. Always add the vmemmap
> pages to this list and let the caller (hugetlb_vmemmap_optimize and
> hugetlb_vmemmap_optimize_folios) to help us to free them. It will be
> clear to me.

Makes sense.

I will update all these in next version based on your suggestions.

Thank you,
-- 
Mike Kravetz

> 
> >    *
> >    * Return: %0 on success, negative error code otherwise.
> >    */
> >   static int vmemmap_remap_free(unsigned long start, unsigned long end,
> > -			      unsigned long reuse)
> > +			      unsigned long reuse,
> > +			      struct list_head *bulk_pages)
> >   {
> >   	int ret;
> >   	LIST_HEAD(vmemmap_pages);
> > @@ -372,7 +375,14 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
> >   	}
> >   	mmap_read_unlock(&init_mm);
> > -	free_vmemmap_page_list(&vmemmap_pages);
> > +	/*
> > +	 * if performing bulk operation, do not free pages here.
> > +	 * rather add them to the bulk list
> > +	 */
> > +	if (!bulk_pages)
> > +		free_vmemmap_page_list(&vmemmap_pages);
> > +	else
> > +		list_splice(&vmemmap_pages, bulk_pages);
> 
> Here, always add vmemmap_pages to the list.
> 
> >   	return ret;
> >   }
> > @@ -546,17 +556,9 @@ static bool vmemmap_should_optimize(const struct hstate *h, const struct page *h
> >   	return true;
> >   }
> > -/**
> > - * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
> > - * @h:		struct hstate.
> > - * @head:	the head page whose vmemmap pages will be optimized.
> > - *
> > - * This function only tries to optimize @head's vmemmap pages and does not
> > - * guarantee that the optimization will succeed after it returns. The caller
> > - * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
> > - * have been optimized.
> > - */
> > -void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> > +static void __hugetlb_vmemmap_optimize(const struct hstate *h,
> > +					struct page *head,
> > +					struct list_head *bulk_pages)
> 
> Also struct list_head *vmemmap_pages.
> 
> >   {
> >   	unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
> >   	unsigned long vmemmap_reuse;
> > @@ -575,18 +577,42 @@ void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> >   	 * to the page which @vmemmap_reuse is mapped to, then free the pages
> >   	 * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
> >   	 */
> > -	if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
> > +	if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse, bulk_pages))
> >   		static_branch_dec(&hugetlb_optimize_vmemmap_key);
> >   	else
> >   		SetHPageVmemmapOptimized(head);
> >   }
> > +/**
> > + * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
> > + * @h:		struct hstate.
> > + * @head:	the head page whose vmemmap pages will be optimized.
> > + *
> > + * This function only tries to optimize @head's vmemmap pages and does not
> > + * guarantee that the optimization will succeed after it returns. The caller
> > + * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
> > + * have been optimized.
> > + */
> > +void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> > +{
> > +	__hugetlb_vmemmap_optimize(h, head, NULL);
> 
> Use free_vmemmap_page_list to free vmemmap pages here.
> 
> > +}
> > +
> > +void hugetlb_vmemmap_optimize_bulk(const struct hstate *h, struct page *head,
> > +			struct list_head *bulk_pages)
> > +{
> > +	__hugetlb_vmemmap_optimize(h, head, bulk_pages);
> > +}
> > +
> >   void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
> >   {
> >   	struct folio *folio;
> > +	LIST_HEAD(vmemmap_pages);
> >   	list_for_each_entry(folio, folio_list, lru)
> > -		hugetlb_vmemmap_optimize(h, &folio->page);
> > +		hugetlb_vmemmap_optimize_bulk(h, &folio->page, &vmemmap_pages);
> 
> Directly use __hugetlb_vmemmap_optimize and delete
> hugetlb_vmemmap_optimize_bulk.
> In the future, we could rename hugetlb_vmemmap_optimize to
> hugetlb_vmemmap_optimize_folio,
> then, both function names are more consistent. E.g.
> 
>   1) hugetlb_vmemmap_optimize_folio(): used to free one folio's vmemmap
> pages.
>   2) hugetlb_vmemmap_optimize_folios(): used to free multiple folio's
> vmemmap pages.
> 
> Thanks.
> 
> > +
> > +	free_vmemmap_page_list(&vmemmap_pages);
> >   }
> >   static struct ctl_table hugetlb_vmemmap_sysctls[] = {
>