diff mbox series

[v2,9/9] x86/clear_huge_page: make clear_contig_region() preemptible

Message ID 20230830184958.2333078-10-ankur.a.arora@oracle.com (mailing list archive)
State New
Headers show
Series x86/clear_huge_page: multi-page clearing | expand

Commit Message

Ankur Arora Aug. 30, 2023, 6:49 p.m. UTC 
clear_contig_region() can be used for clearing  regions as large as a
gigantic page. Allow preemption in irqentry_exit to make sure we don't
hold on to the CPU for an arbitrarily long period.

Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 arch/x86/mm/hugetlbpage.c | 5 +++++
 1 file changed, 5 insertions(+)

Comments

Peter Zijlstra Sept. 8, 2023, 12:45 p.m. UTC | #1 
On Wed, Aug 30, 2023 at 11:49:58AM -0700, Ankur Arora wrote:
> clear_contig_region() can be used for clearing  regions as large as a
> gigantic page. Allow preemption in irqentry_exit to make sure we don't
> hold on to the CPU for an arbitrarily long period.

It would be very nice to quantify the latency improvement here. At the
very least perhaps mention how long a 2M or 1G clear takes (on you
favourite machine) to illustrate why this is needed.

> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
>  arch/x86/mm/hugetlbpage.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
> index 0b9f7a6dad93..55d1d15ea618 100644
> --- a/arch/x86/mm/hugetlbpage.c
> +++ b/arch/x86/mm/hugetlbpage.c
> @@ -152,7 +152,12 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>  #ifndef CONFIG_HIGHMEM
>  static void clear_contig_region(struct page *page, unsigned int npages)
>  {
> +	/*
> +	 * We might be clearing a large region. Allow rescheduling.
> +	 */
> +	allow_resched();
>  	clear_pages(page_address(page), npages);
> +	disallow_resched();
>  }

Why is this in clear_contig_region() and not clear_pages() ? Any other
clear_pages() user will have the same problems no?
diff mbox series

Patch

diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c
index 0b9f7a6dad93..55d1d15ea618 100644
--- a/arch/x86/mm/hugetlbpage.c
+++ b/arch/x86/mm/hugetlbpage.c
@@ -152,7 +152,12 @@  hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 #ifndef CONFIG_HIGHMEM
 static void clear_contig_region(struct page *page, unsigned int npages)
 {
+	/*
+	 * We might be clearing a large region. Allow rescheduling.
+	 */
+	allow_resched();
 	clear_pages(page_address(page), npages);
+	disallow_resched();
 }
 
 /*