The patch titled
Subject: mm,page_owner: fix accounting of pages when migrating
has been added to the -mm mm-unstable branch. Its filename is
mmpage_owner-fix-accounting-of-pages-when-migrating.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmpage_owner-fix-accounting-of-pages-when-migrating.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: Oscar Salvador <osalvador@xxxxxxx>
Subject: mm,page_owner: fix accounting of pages when migrating
Date: Tue, 26 Mar 2024 07:30:36 +0100
Upon migration, new allocated pages are being given the handle of the old
pages. This is problematic because it means that for the stack which
allocated the old page, we will be substracting the old page + the new one
when that page is freed, creating an accounting imbalance.
There is an interest in keeping it that way, as otherwise the output will
biased towards migration stacks should those operations occur often, but
that is not really helpful.
The link from the new page to the old stack is being performed by calling
__update_page_owner_handle() in __folio_copy_owner(). The only thing that
is left is to link the migrate stack to the old page, so the old page will
be subtracted from the migrate stack, avoiding by doing so any possible
imbalance.
Link: https://lkml.kernel.org/r/20240326063036.6242-4-osalvador@xxxxxxx
Fixes: 217b2119b9e2 ("mm,page_owner: implement the tracking of the stacks count")
Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_owner.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
--- a/mm/page_owner.c~mmpage_owner-fix-accounting-of-pages-when-migrating
+++ a/mm/page_owner.c
@@ -366,9 +366,12 @@ void __split_page_owner(struct page *pag
void __folio_copy_owner(struct folio *newfolio, struct folio *old)
{
+ int i;
struct page_ext *old_ext;
struct page_ext *new_ext;
struct page_owner *old_page_owner;
+ struct page_owner *new_page_owner;
+ depot_stack_handle_t migrate_handle;
old_ext = page_ext_get(&old->page);
if (unlikely(!old_ext))
@@ -381,6 +384,8 @@ void __folio_copy_owner(struct folio *ne
}
old_page_owner = get_page_owner(old_ext);
+ new_page_owner = get_page_owner(new_ext);
+ migrate_handle = new_page_owner->handle;
__update_page_owner_handle(new_ext, old_page_owner->handle,
old_page_owner->order, old_page_owner->gfp_mask,
old_page_owner->last_migrate_reason,
@@ -395,6 +400,16 @@ void __folio_copy_owner(struct folio *ne
old_page_owner->free_pid,
old_page_owner->free_tgid,
old_page_owner->free_ts_nsec);
+ /*
+ * We linked the original stack to the new folio, we need to do the same
+ * for the new one and the old folio otherwise there will be an imbalance
+ * when subtracting those pages from the stack.
+ */
+ for (i = 0; i < (1 << new_page_owner->order); i++) {
+ old_page_owner->handle = migrate_handle;
+ old_ext = page_ext_next(old_ext);
+ old_page_owner = get_page_owner(old_ext);
+ }
page_ext_put(new_ext);
page_ext_put(old_ext);
_
Patches currently in -mm which might be from osalvador@xxxxxxx are
mmpage_owner-update-metada-for-tail-pages.patch
mmpage_owner-fix-refcount-imbalance.patch
mmpage_owner-fix-accounting-of-pages-when-migrating.patch
