[PATCH 1/4] mm: vmpressure: scale sampling window with machine size

[PATCH 1/4] mm: vmpressure: scale sampling window with machine size

[deepakraog]

The vmpressure window size was fixed at 512 pages (SWAP_CLUSTER_MAX * 16).
Scale it at boot from total memory and CPU count using the same fls-based
formula as vmstat per-zone thresholds, clamped between 128 and 2048 pages.

Signed-off-by: deepakraog <gaikwad.dcg@gmail.com>
---
 mm/vmpressure.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index f053554e5..8925d4ad3 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -33,9 +33,29 @@
  * SWAP_CLUSTER_MAX, it makes sense to use it for the window size as well.
  *
  * TODO: Make the window size depend on machine size, as we do for vmstat
- * thresholds. Currently we set it to 512 pages (2MB for 4KB pages).
+ * thresholds. Scales with CPU count and total memory at boot.
  */
-static const unsigned long vmpressure_win = SWAP_CLUSTER_MAX * 16;
+static unsigned long vmpressure_win;
+
+static unsigned long __init vmpressure_window_size(void)
+{
+	unsigned long win;
+	int mem;
+
+	mem = totalram_pages() >> (27 - PAGE_SHIFT);
+	win = SWAP_CLUSTER_MAX * (unsigned long)fls(num_online_cpus()) *
+	      (1 + fls(mem));
+	win = max(win, SWAP_CLUSTER_MAX * 4UL);
+	win = min(win, SWAP_CLUSTER_MAX * 64UL);
+	return win;
+}
+
+static int __init vmpressure_win_init(void)
+{
+	vmpressure_win = vmpressure_window_size();
+	return 0;
+}
+core_initcall(vmpressure_win_init);
 
 /*
  * These thresholds are used when we account memory pressure through
-- 
Deepak Rao Gaikwad

[PATCH 3/4] mm: vrealloc: grow vm_area mappings in place

[deepakraog]

When vrealloc() needs more pages than are currently mapped, allocate and
map additional pages at the end of the existing vm_area instead of
always allocating a new area and memcpy()'ing. Fall back to the
existing realloc path when in-place grow is not possible.

Signed-off-by: deepakraog <gaikwad.dcg@gmail.com>
---
 mm/vmalloc.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 1afca3568..46cf10c62 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4426,8 +4426,56 @@ void *vrealloc_node_align_noprof(const void *p, size_t size, unsigned long align
 		return (void *)p;
 	}
 
+	{
+		unsigned int new_nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT;
+		unsigned int old_nr_pages = vm->nr_pages;
+
+		if (new_nr_pages > old_nr_pages && !vm_area_page_order(vm) &&
+		    !(vm->flags & (VM_FLUSH_RESET_PERMS | VM_USERMAP)) &&
+		    gfp_has_io_fs(flags)) {
+			unsigned int extra = new_nr_pages - old_nr_pages;
+			unsigned long addr = (unsigned long)kasan_reset_tag(p);
+			struct vmap_node *vn = addr_to_node(addr);
+			struct page **pages;
+			int ret;
+
+			pages = kvmalloc_array(extra, sizeof(struct page *), gfp);
+			if (!pages)
+				goto need_realloc;
+
+			if (vm_area_alloc_pages(vmalloc_gfp_adjust(gfp, 0), nid,
+						0, extra, pages) != extra) {
+				kvfree(pages);
+				goto need_realloc;
+			}
+
+			spin_lock(&vn->busy.lock);
+			ret = vmap_pages_range(addr + ((unsigned long)old_nr_pages
+						       << PAGE_SHIFT),
+					       addr + ((unsigned long)new_nr_pages
+						       << PAGE_SHIFT),
+					       PAGE_KERNEL, pages, PAGE_SHIFT);
+			spin_unlock(&vn->busy.lock);
+			if (ret < 0) {
+				free_pages_bulk(pages, extra);
+				kvfree(pages);
+				goto need_realloc;
+			}
+
+			memcpy(&vm->pages[old_nr_pages], pages,
+			       extra * sizeof(struct page *));
+			kvfree(pages);
+			vm->nr_pages = new_nr_pages;
+			vm->requested_size = size;
+			kasan_vrealloc(p, old_size, size);
+			if (want_init_on_alloc(flags))
+				memset((void *)p + old_size, 0, size - old_size);
+			return (void *)p;
+		}
+	}
+
 need_realloc:
-	/* TODO: Grow the vm_area, i.e. allocate and map additional pages. */
+	/* Fall back to a fresh vm_area when in-place grow is not possible. */
 	n = __vmalloc_node_noprof(size, align, flags, nid, __builtin_return_address(0));
 
 	if (!n)
-- 
Deepak Rao Gaikwad

Re: [PATCH 1/4] mm: vmpressure: scale sampling window with machine size

[Michal Hocko]

On Wed 15-07-26 20:06:41, deepakraog wrote:
> The vmpressure window size was fixed at 512 pages (SWAP_CLUSTER_MAX * 16).
> Scale it at boot from total memory and CPU count using the same fls-based
> formula as vmstat per-zone thresholds, clamped between 128 and 2048 pages.

This is not giving us any rationale why this is needed or desirable.

-- 
Michal Hocko
SUSE Labs

Re: [PATCH 1/4] mm: vmpressure: scale sampling window with machine size

[Lorenzo Stoakes (ARM)]

On Wed, Jul 22, 2026 at 10:07:53AM +0200, Michal Hocko wrote:
> On Wed 15-07-26 20:06:41, deepakraog wrote:
> > The vmpressure window size was fixed at 512 pages (SWAP_CLUSTER_MAX * 16).
> > Scale it at boot from total memory and CPU count using the same fls-based
> > formula as vmstat per-zone thresholds, clamped between 128 and 2048 pages.
>
> This is not giving us any rationale why this is needed or desirable.

Agreed, the series are all somewhat corrupted here (seemingly some patches
missing + not sent to the same list of people, unrelated stuff in the same
series, etc.).

I replied to the v2 of this ([0]), in general this is essentially the same thing
submitted by a previous person ([1]), and Deepak acked that ([2]) and agreed
that this isn't worth pursuing.

Cheers, Lorenzo

[0]:https://lore.kernel.org/linux-mm/aljYxLusTzZkTfnH@lucifer/
[1]:https://lore.kernel.org/all/20260227221555.29969-1-mcq@disroot.org/
[2]:https://lore.kernel.org/all/20260716134938.42495-1-gaikwad.dcg@gmail.com/

>
> --
> Michal Hocko
> SUSE Labs