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Message-Id: <20240617142951.08a9cdc791c8edeeca50509b@linux-foundation.org>
Date: Mon, 17 Jun 2024 14:29:51 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Stephen Brennan <stephen.s.brennan@...cle.com>
Cc: linux-mm@...ck.org, Vlastimil Babka <vbabka@...e.cz>,
"Vishal Moola (Oracle)" <vishal.moola@...il.com>, Omar Sandoval
<osandov@...ndov.com>, David Hildenbrand <david@...hat.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>, Hao Ge <gehao@...inos.cn>,
linux-debuggers@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mm: convert page type macros to enum
On Mon, 17 Jun 2024 13:34:21 -0700 Stephen Brennan <stephen.s.brennan@...cle.com> wrote:
> >>> Fixes: 46df8e73a4a3 ("mm: free up PG_slab")
> >>
> >> Should we backport this into 6.9.x?
> >
> > Hi Andrew,
> >
> > Looks like commit 46df8e73a4a3 ("mm: free up PG_slab") is introduced in
> > the v6.10-rc's, and not backported to 6.9. So PG_slab is still part of
>
> Hi Andrew,
>
> I saw that you've merged this into mm-unstable, thank you!
>
> Since 46df8e73a4a3 ("mm: free up PG_slab") is part of the current 6.10
> RC, it would be great if this patch could be part of the 6.10 release so
> we don't release a kernel missing the PG_slab info.
>
> Can you confirm if mm-unstable will get merged in this release cycle? Or
> else, would it be possible to include it in a branch that will?
Turns out the patch as sent was based on David's "mm: allow reuse of
the lower 16 bit of the page type with an actual type", which changed
the page flags a lot, I redid this patch thusly:
--- a/include/linux/page-flags.h~mm-convert-page-type-macros-to-enum
+++ a/include/linux/page-flags.h
@@ -944,15 +944,22 @@ PAGEFLAG_FALSE(HasHWPoisoned, has_hwpois
* mistaken for a page type value.
*/
-#define PAGE_TYPE_BASE 0xf0000000
-/* Reserve 0x0000007f to catch underflows of _mapcount */
-#define PAGE_MAPCOUNT_RESERVE -128
-#define PG_buddy 0x00000080
-#define PG_offline 0x00000100
-#define PG_table 0x00000200
-#define PG_guard 0x00000400
-#define PG_hugetlb 0x00000800
-#define PG_slab 0x00001000
+enum pagetype {
+ /*
+ * Reserve 0xffff0000 - 0xfffffffe to catch _mapcount underflows and
+ * allow owners that set a type to reuse the lower 16 bit for their own
+ * purposes.
+ */
+ PG_buddy = 0x00000080,
+ PG_offline = 0x00000100,
+ PG_table = 0x00000200,
+ PG_guard = 0x00000400,
+ PG_hugetlb = 0x00000800,
+ PG_slab = 0x00001000,
+
+ PAGE_TYPE_BASE = 0xf0000000,
+ PAGE_MAPCOUNT_RESERVE = -128,
+};
#define PageType(page, flag) \
((page->page_type & (PAGE_TYPE_BASE | flag)) == PAGE_TYPE_BASE)
_
(please check carefully)
and David's later "mm: allow reuse of the lower 16 bit of the page type
with an actual type" becomes
include/linux/mm_types.h | 5 +++++
include/linux/page-flags.h | 16 ++++++++--------
2 files changed, 13 insertions(+), 8 deletions(-)
--- a/include/linux/mm_types.h~mm-allow-reuse-of-the-lower-16-bit-of-the-page-type-with-an-actual-type
+++ a/include/linux/mm_types.h
@@ -157,6 +157,11 @@ struct page {
*
* See page-flags.h for a list of page types which are currently
* stored here.
+ *
+ * Owners of typed folios may reuse the lower 16 bit of the
+ * head page page_type field after setting the page type,
+ * but must reset these 16 bit to -1 before clearing the
+ * page type.
*/
unsigned int page_type;
--- a/include/linux/page-flags.h~mm-allow-reuse-of-the-lower-16-bit-of-the-page-type-with-an-actual-type
+++ a/include/linux/page-flags.h
@@ -951,15 +951,15 @@ enum pagetype {
* allow owners that set a type to reuse the lower 16 bit for their own
* purposes.
*/
- PG_buddy = 0x00000080,
- PG_offline = 0x00000100,
- PG_table = 0x00000200,
- PG_guard = 0x00000400,
- PG_hugetlb = 0x00000800,
- PG_slab = 0x00001000,
+ PG_buddy = 0x40000000,
+ PG_offline = 0x20000000,
+ PG_table = 0x10000000,
+ PG_guard = 0x08000000,
+ PG_hugetlb = 0x04008000,
+ PG_slab = 0x02000000,
- PAGE_TYPE_BASE = 0xf0000000,
- PAGE_MAPCOUNT_RESERVE = -128,
+ PAGE_TYPE_BASE = 0x80000000,
+ PAGE_MAPCOUNT_RESERVE = (~0x0000ffff),
};
#define PageType(page, flag) \
_
and that patch's fixup becomes
--- a/include/linux/page-flags.h~mm-allow-reuse-of-the-lower-16-bit-of-the-page-type-with-an-actual-type-fix
+++ a/include/linux/page-flags.h
@@ -955,7 +955,7 @@ enum pagetype {
PG_offline = 0x20000000,
PG_table = 0x10000000,
PG_guard = 0x08000000,
- PG_hugetlb = 0x04008000,
+ PG_hugetlb = 0x04000000,
PG_slab = 0x02000000,
PAGE_TYPE_BASE = 0x80000000,
_
and "mm/zsmalloc: use a proper page type" becomes, in part,
--- a/include/linux/page-flags.h~mm-zsmalloc-use-a-proper-page-type
+++ a/include/linux/page-flags.h
@@ -957,6 +957,7 @@ enum pagetype {
PG_guard = 0x08000000,
PG_hugetlb = 0x04000000,
PG_slab = 0x02000000,
+ PG_zsmalloc = 0x01000000,
PAGE_TYPE_BASE = 0x80000000,
PAGE_MAPCOUNT_RESERVE = (~0x0000ffff),
and the end result is identical to yesterday's mm-everything so that's
all good.
However I wouldn't want to send the altered version of "mm: convert
page type macros to enum" into 6.10-rcX because it gets so altered by
David's mm-unstable changes for the next merge window. The new version
of the hotfixes patch won't have had any valid testing on its own.
So I'll temporarily drop David's "mm: page_type, zsmalloc and
page_mapcount_reset()" series from mm-unstable. To permit the new "mm:
convert page type macros to enum" to get some linux-next exposure.
David, please remind me to restore that series in a week or so?
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