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    SubjectRe: [PATCH v2 08/11] hugetlb: batch freeing of vmemmap pages
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    On 2023/9/6 05:44, 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 | 60 ++++++++++++++++++++++++++++----------------
    > 1 file changed, 38 insertions(+), 22 deletions(-)
    >
    > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
    > index 79de984919ef..a715712df831 100644
    > --- a/mm/hugetlb_vmemmap.c
    > +++ b/mm/hugetlb_vmemmap.c
    > @@ -306,18 +306,21 @@ 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.
    > + * @vmemmap_pages: list to deposit vmemmap pages to be freed. It is callers
    > + * responsibility to free pages.
    > *
    > * 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 *vmemmap_pages)
    > {
    > int ret;
    > - LIST_HEAD(vmemmap_pages);
    > + LIST_HEAD(freed_pages);

    IIUC, we could reuse the parameter of @vmemmap_pages directly instead of
    a temporary variable, could it be dropped?

    > struct vmemmap_remap_walk walk = {
    > .remap_pte = vmemmap_remap_pte,
    > .reuse_addr = reuse,
    > - .vmemmap_pages = &vmemmap_pages,
    > + .vmemmap_pages = &freed_pages,
    > };
    > int nid = page_to_nid((struct page *)start);
    > gfp_t gfp_mask = GFP_KERNEL | __GFP_THISNODE | __GFP_NORETRY |
    > @@ -335,7 +338,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
    > if (walk.reuse_page) {
    > copy_page(page_to_virt(walk.reuse_page),
    > (void *)walk.reuse_addr);
    > - list_add(&walk.reuse_page->lru, &vmemmap_pages);
    > + list_add(&walk.reuse_page->lru, &freed_pages);
    > }
    >
    > /*
    > @@ -366,15 +369,14 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
    > walk = (struct vmemmap_remap_walk) {
    > .remap_pte = vmemmap_restore_pte,
    > .reuse_addr = reuse,
    > - .vmemmap_pages = &vmemmap_pages,
    > + .vmemmap_pages = &freed_pages,
    > };
    >
    > vmemmap_remap_range(reuse, end, &walk);
    > }
    > mmap_read_unlock(&init_mm);
    >
    > - free_vmemmap_page_list(&vmemmap_pages);
    > -
    > + list_splice(&freed_pages, vmemmap_pages);
    > return ret;
    > }
    >
    > @@ -553,17 +555,9 @@ 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 *vmemmap_pages)
    > {
    > unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
    > unsigned long vmemmap_reuse;
    > @@ -580,21 +574,43 @@ void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
    >
    > /*
    > * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
    > - * to the page which @vmemmap_reuse is mapped to, then free the pages
    > - * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
    > + * to the page which @vmemmap_reuse is mapped to. Add pages previously
    > + * mapping the range to vmemmap_pages list so that they can be freed by
    > + * the caller.
    > */
    > - if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
    > + if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse, vmemmap_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)
    > +{
    > + LIST_HEAD(vmemmap_pages);
    > +
    > + __hugetlb_vmemmap_optimize(h, head, &vmemmap_pages);
    > + free_vmemmap_page_list(&vmemmap_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(h, &folio->page, &vmemmap_pages);
    > +
    > + free_vmemmap_page_list(&vmemmap_pages);
    > }
    >
    > static struct ctl_table hugetlb_vmemmap_sysctls[] = {

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