The patch titled
Subject: mm: page_ext: make lookup_page_ext() public
has been added to the -mm mm-unstable branch. Its filename is
mm-page_ext-make-lookup_page_ext-public.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_ext-make-lookup_page_ext-public.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Luiz Capitulino <luizcap@xxxxxxxxxx>
Subject: mm: page_ext: make lookup_page_ext() public
Date: Mon, 24 Feb 2025 16:59:05 -0500
Patch series "mm: page_ext: Introduce new iteration API", v2.
Introduction
============
[ Thanks to David Hildenbrand for identifying the root cause of this
issue and proving guidance on how to fix it. The new API idea, bugs
and misconceptions are all mine though ]
Currently, trying to reserve 1G pages with page_owner=on and sparsemem
causes a crash. The reproducer is very simple:
1. Build the kernel with CONFIG_SPARSEMEM=y and the table extensions
2. Pass 'default_hugepagesz=1 page_owner=on' in the kernel command-line
3. Reserve one 1G page at run-time, this should crash (see patch 1 for
backtrace)
[ A crash with page_table_check is also possible, but harder to trigger ]
Apparently, starting with commit cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP
for gigantic folios") we now pass the full allocation order to page
extension clients and the page extension implementation assumes that all
PFNs of an allocation range will be stored in the same memory section
(which is not true for 1G pages).
To fix this, this series introduces a new iteration API for page extension
objects. The API checks if the next page extension object can be
retrieved from the current section or if it needs to look up for it in
another section.
Please find all details in patch 2.
This patch (of 4):
The next commit will use lookup_page_ext().
Link: https://lkml.kernel.org/r/cover.1740434344.git.luizcap@xxxxxxxxxx
Link: https://lkml.kernel.org/r/fb46436ec9ef892b6f40b9e48d40237b9855ac16.1740434344.git.luizcap@xxxxxxxxxx
Signed-off-by: Luiz Capitulino <luizcap@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/page_ext.h | 1 +
mm/page_ext.c | 4 ++--
2 files changed, 3 insertions(+), 2 deletions(-)
--- a/include/linux/page_ext.h~mm-page_ext-make-lookup_page_ext-public
+++ a/include/linux/page_ext.h
@@ -79,6 +79,7 @@ static inline void page_ext_init(void)
extern struct page_ext *page_ext_get(const struct page *page);
extern void page_ext_put(struct page_ext *page_ext);
+extern struct page_ext *lookup_page_ext(const struct page *page);
static inline void *page_ext_data(struct page_ext *page_ext,
struct page_ext_operations *ops)
--- a/mm/page_ext.c~mm-page_ext-make-lookup_page_ext-public
+++ a/mm/page_ext.c
@@ -165,7 +165,7 @@ void __meminit pgdat_page_ext_init(struc
pgdat->node_page_ext = NULL;
}
-static struct page_ext *lookup_page_ext(const struct page *page)
+struct page_ext *lookup_page_ext(const struct page *page)
{
unsigned long pfn = page_to_pfn(page);
unsigned long index;
@@ -245,7 +245,7 @@ static bool page_ext_invalid(struct page
return !page_ext || (((unsigned long)page_ext & PAGE_EXT_INVALID) == PAGE_EXT_INVALID);
}
-static struct page_ext *lookup_page_ext(const struct page *page)
+struct page_ext *lookup_page_ext(const struct page *page)
{
unsigned long pfn = page_to_pfn(page);
struct mem_section *section = __pfn_to_section(pfn);
_
Patches currently in -mm which might be from luizcap@xxxxxxxxxx are
mm-page_ext-make-lookup_page_ext-public.patch
mm-page_ext-add-an-iteration-api-for-page-extensions.patch
mm-page_table_check-use-new-iteration-api.patch
mm-page_owner-use-new-iteration-api.patch
