+ mm-vmallocc-find-the-vmap-of-vmap_nodes-in-reverse-order.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/vmalloc.c: find the vmap of vmap_nodes in reverse order
has been added to the -mm mm-new branch.  Its filename is
     mm-vmallocc-find-the-vmap-of-vmap_nodes-in-reverse-order.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmallocc-find-the-vmap-of-vmap_nodes-in-reverse-order.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Baoquan He <bhe@redhat.com>
Subject: mm/vmalloc.c: find the vmap of vmap_nodes in reverse order
Date: Sat, 19 Apr 2025 06:36:50 +0800

When finding VA in vn->busy, if VA spans several zones and the passed addr
is not the same as va->va_start, we should scan the vn in reverse odrdr
because the starting address of VA must be smaller than the passed addr if
it really resides in the VA.

E.g on a system nr_vmap_nodes=100,

     <----va---->
 -|-----|-----|-----|-----|-----|-----|-----|-----|-----|-
    ...   n-1   n    n+1   n+2   ...   100     0     1

VA resides in node 'n' whereas it spans 'n', 'n+1' and 'n+2'.  If passed
addr is within 'n+2', we should try nodes backwards on 'n+1' and 'n', then
succeed very soon.

Meanwhile we still need loop around because VA could spans node from 'n'
to node 100, node 0, node 1.

Anyway, changing to find in reverse order can improve efficiency on many
CPUs system.

Link: https://lkml.kernel.org/r/20250418223653.243436-3-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Shivank Garg <shivankg@amd.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmalloc.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/vmalloc.c~mm-vmallocc-find-the-vmap-of-vmap_nodes-in-reverse-order
+++ a/mm/vmalloc.c
@@ -2435,7 +2435,7 @@ struct vmap_area *find_vmap_area(unsigne
 
 		if (va)
 			return va;
-	} while ((i = (i + 1) % nr_vmap_nodes) != j);
+	} while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j);
 
 	return NULL;
 }
@@ -2461,7 +2461,7 @@ static struct vmap_area *find_unlink_vma
 
 		if (va)
 			return va;
-	} while ((i = (i + 1) % nr_vmap_nodes) != j);
+	} while ((i = (i + nr_vmap_nodes - 1) % nr_vmap_nodes) != j);
 
 	return NULL;
 }
_

Patches currently in -mm which might be from bhe@redhat.com are

mm-gup-remove-unneeded-checking-in-follow_page_pte.patch
mm-gup-remove-gup_fast_pgd_leaf-and-clean-up-the-relevant-codes.patch
mm-gup-clean-up-codes-in-fault_in_xxx-functions.patch
mm-gup-clean-up-codes-in-fault_in_xxx-functions-v5.patch
mm-vmallocc-change-purge_ndoes-as-local-static-variable.patch
mm-vmallocc-find-the-vmap-of-vmap_nodes-in-reverse-order.patch
mm-vmallocc-optimize-code-in-decay_va_pool_node-a-little-bit.patch
mm-vmalloc-optimize-function-vm_unmap_aliases.patch
mm-vmallocc-return-explicit-error-value-in-alloc_vmap_area.patch