The quilt patch titled
Subject: mm/page_alloc: remove prefetchw() on freeing page to buddy system
has been removed from the -mm tree. Its filename was
mm-page_alloc-remove-prefetchw-on-freeing-page-to-buddy-system.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Wei Yang <richard.weiyang@xxxxxxxxx>
Subject: mm/page_alloc: remove prefetchw() on freeing page to buddy system
Date: Tue, 2 Jul 2024 02:09:31 +0000
The prefetchw() is introduced from an ancient patch[1].
The change log says:
The basic idea is to free higher order pages instead of going
through every single one. Also, some unnecessary atomic operations
are done away with and replaced with non-atomic equivalents, and
prefetching is done where it helps the most. For a more in-depth
discusion of this patch, please see the linux-ia64 archives (topic
is "free bootmem feedback patch").
So there are several changes improve the bootmem freeing, in which the
most basic idea is freeing higher order pages. And as Matthew says,
"Itanium CPUs of this era had no prefetchers."
I did 10 round bootup tests before and after this change, the data doesn't
prove prefetchw() help speeding up bootmem freeing. The sum of the 10
round bootmem freeing time after prefetchw() removal even 5.2% faster than
before.
[1]: https://lore.kernel.org/linux-ia64/40F46962.4090604@xxxxxxx/
Link: https://lkml.kernel.org/r/20240702020931.7061-1-richard.weiyang@xxxxxxxxx
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-remove-prefetchw-on-freeing-page-to-buddy-system
+++ a/mm/page_alloc.c
@@ -1236,16 +1236,11 @@ void __free_pages_core(struct page *page
*/
if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) &&
unlikely(context == MEMINIT_HOTPLUG)) {
- prefetchw(p);
- for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
- prefetchw(p + 1);
+ for (loop = 0; loop < nr_pages; loop++, p++) {
VM_WARN_ON_ONCE(PageReserved(p));
__ClearPageOffline(p);
set_page_count(p, 0);
}
- VM_WARN_ON_ONCE(PageReserved(p));
- __ClearPageOffline(p);
- set_page_count(p, 0);
/*
* Freeing the page with debug_pagealloc enabled will try to
@@ -1255,14 +1250,10 @@ void __free_pages_core(struct page *page
debug_pagealloc_map_pages(page, nr_pages);
adjust_managed_page_count(page, nr_pages);
} else {
- prefetchw(p);
- for (loop = 0; loop < (nr_pages - 1); loop++, p++) {
- prefetchw(p + 1);
+ for (loop = 0; loop < nr_pages; loop++, p++) {
__ClearPageReserved(p);
set_page_count(p, 0);
}
- __ClearPageReserved(p);
- set_page_count(p, 0);
/* memblock adjusts totalram_pages() manually. */
atomic_long_add(nr_pages, &page_zone(page)->managed_pages);
_
Patches currently in -mm which might be from richard.weiyang@xxxxxxxxx are
mm-page_alloc-put-__free_pages_core-in-__meminit-section.patch
mm-use-zonelist_zone-to-get-zone.patch
