+ mm-hugeltb-fix-nodes-huge-page-allocation-when-there-are-surplus-pages.patch added to mm-unstable branch

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

The patch titled
     Subject: mm/hugeltb: fix nodes huge page allocation when there are surplus pages
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hugeltb-fix-nodes-huge-page-allocation-when-there-are-surplus-pages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugeltb-fix-nodes-huge-page-allocation-when-there-are-surplus-pages.patch

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Xueshi Hu <xueshi.hu@smartx.com>
Subject: mm/hugeltb: fix nodes huge page allocation when there are surplus pages
Date: Tue, 29 Aug 2023 11:33:43 +0800

In set_nr_huge_pages(), local variable "count" is used to record
persistent_huge_pages(), but when it cames to nodes huge page allocation,
the semantics changes to nr_huge_pages.  When there exists surplus huge
pages and using the interface under
/sys/devices/system/node/node*/hugepages to change huge page pool size,
this difference can result in the allocation of an unexpected number of
huge pages.

Steps to reproduce the bug:

Starting with:

				  Node 0          Node 1    Total
	HugePages_Total             0.00            0.00     0.00
	HugePages_Free              0.00            0.00     0.00
	HugePages_Surp              0.00            0.00     0.00

create 100 huge pages in Node 0 and consume it, then set Node 0 's
nr_hugepages to 0.

yields:

				  Node 0          Node 1    Total
	HugePages_Total           200.00            0.00   200.00
	HugePages_Free              0.00            0.00     0.00
	HugePages_Surp            200.00            0.00   200.00

write 100 to Node 1's nr_hugepages

		echo 100 > /sys/devices/system/node/node1/\
	hugepages/hugepages-2048kB/nr_hugepages

gets:

				  Node 0          Node 1    Total
	HugePages_Total           200.00          400.00   600.00
	HugePages_Free              0.00          400.00   400.00
	HugePages_Surp            200.00            0.00   200.00

Kernel is expected to create only 100 huge pages and it gives 200.

Link: https://lkml.kernel.org/r/20230829033343.467779-1-xueshi.hu@smartx.com
Fixes: 9a30523066cd ("hugetlb: add per node hstate attributes")
Signed-off-by: Xueshi Hu <xueshi.hu@smartx.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/hugetlb.c~mm-hugeltb-fix-nodes-huge-page-allocation-when-there-are-surplus-pages
+++ a/mm/hugetlb.c
@@ -3457,7 +3457,9 @@ static int set_max_huge_pages(struct hst
 	if (nid != NUMA_NO_NODE) {
 		unsigned long old_count = count;
 
-		count += h->nr_huge_pages - h->nr_huge_pages_node[nid];
+		count += persistent_huge_pages(h) -
+			 (h->nr_huge_pages_node[nid] -
+			  h->surplus_huge_pages_node[nid]);
 		/*
 		 * User may have specified a large count value which caused the
 		 * above calculation to overflow.  In this case, they wanted
_

Patches currently in -mm which might be from xueshi.hu@smartx.com are

mm-hugeltb-fix-nodes-huge-page-allocation-when-there-are-surplus-pages.patch