The patch titled
Subject: mm/highmem: reimplement totalhigh_pages() by walking zones
has been added to the -mm mm-unstable branch. Its filename is
mm-highmem-reimplement-totalhigh_pages-by-walking-zones.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-highmem-reimplement-totalhigh_pages-by-walking-zones.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/highmem: reimplement totalhigh_pages() by walking zones
Date: Fri, 7 Jun 2024 10:37:10 +0200
Patch series "mm/highmem: don't track highmem pages manually".
Let's remove highmem special-casing from adjust_managed_page_count(), to
result in less confusion why memblock manually adjusts totalram_pages, and
__free_pages_core() only adjusts the zone's managed pages -- what about
the highmem pages that adjust_managed_page_count() updates?
Now, we only maintain totalram_pages and a zone's managed pages
independent of highmem support. We can derive the number of highmem pages
simply by looking at the relevant zone's managed pages. I don't think
there is any particular fast path that needs a maximum-efficient
totalhigh_pages() implementation.
Note that highmem memory is currently initialized using
free_highmem_page()->free_reserved_page(), not __free_pages_core(). In
the future we might want to also use __free_pages_core() to initialize
highmem memory, to make that less special, and consider moving
totalram_pages updates into __free_pages_core() [1], so we can just use
adjust_managed_page_count() in there as well.
Booting a simple kernel in QEMU reveals no highmem accounting change:
Before:
Memory: 3095448K/3145208K available (14802K kernel code, 2073K rwdata,
5000K rodata, 740K init, 556K bss, 49760K reserved, 0K cma-reserved,
2244488K highmem)
After:
Memory: 3095276K/3145208K available (14802K kernel code, 2073K rwdata,
5000K rodata, 740K init, 556K bss, 49932K reserved, 0K cma-reserved,
2244488K highmem)
[1] https://lkml.kernel.org/r/20240601133402.2675-1-richard.weiyang@xxxxxxxxx
This patch (of 2):
Can we get rid of the highmem ifdef in adjust_managed_page_count()?
Likely yes: we don't have that many totalhigh_pages() users, and they all
don't seem to be very performance critical.
So let's implement totalhigh_pages() like nr_free_highpages(), collecting
information from all zones. This is now similar to what we do in
si_meminfo_node() to collect the per-node highmem page count.
In the common case (single node, 3-4 zones), we really shouldn't care. We
could optimize a bit further (only walk ZONE_HIGHMEM and ZONE_MOVABLE if
required), but there doesn't seem a real need for that.
Link: https://lkml.kernel.org/r/20240607083711.62833-1-david@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20240607083711.62833-2-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/highmem-internal.h | 9 ++-------
mm/highmem.c | 16 +++++++++++++---
mm/page_alloc.c | 4 ----
3 files changed, 15 insertions(+), 14 deletions(-)
--- a/include/linux/highmem-internal.h~mm-highmem-reimplement-totalhigh_pages-by-walking-zones
+++ a/include/linux/highmem-internal.h
@@ -132,7 +132,7 @@ static inline void __kunmap_atomic(const
}
unsigned int __nr_free_highpages(void);
-extern atomic_long_t _totalhigh_pages;
+unsigned long __totalhigh_pages(void);
static inline unsigned int nr_free_highpages(void)
{
@@ -141,12 +141,7 @@ static inline unsigned int nr_free_highp
static inline unsigned long totalhigh_pages(void)
{
- return (unsigned long)atomic_long_read(&_totalhigh_pages);
-}
-
-static inline void totalhigh_pages_add(long count)
-{
- atomic_long_add(count, &_totalhigh_pages);
+ return __totalhigh_pages();
}
static inline bool is_kmap_addr(const void *x)
--- a/mm/highmem.c~mm-highmem-reimplement-totalhigh_pages-by-walking-zones
+++ a/mm/highmem.c
@@ -111,9 +111,6 @@ static inline wait_queue_head_t *get_pkm
}
#endif
-atomic_long_t _totalhigh_pages __read_mostly;
-EXPORT_SYMBOL(_totalhigh_pages);
-
unsigned int __nr_free_highpages(void)
{
struct zone *zone;
@@ -125,6 +122,19 @@ unsigned int __nr_free_highpages(void)
}
return pages;
+}
+
+unsigned long __totalhigh_pages(void)
+{
+ unsigned long pages = 0;
+ struct zone *zone;
+
+ for_each_populated_zone(zone) {
+ if (is_highmem(zone))
+ pages += zone_managed_pages(zone);
+ }
+
+ return pages;
}
static int pkmap_count[LAST_PKMAP];
--- a/mm/page_alloc.c~mm-highmem-reimplement-totalhigh_pages-by-walking-zones
+++ a/mm/page_alloc.c
@@ -5785,10 +5785,6 @@ void adjust_managed_page_count(struct pa
{
atomic_long_add(count, &page_zone(page)->managed_pages);
totalram_pages_add(count);
-#ifdef CONFIG_HIGHMEM
- if (PageHighMem(page))
- totalhigh_pages_add(count);
-#endif
}
EXPORT_SYMBOL(adjust_managed_page_count);
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
revert-mm-init_mlocked_on_free_v3.patch
mm-memory-move-page_count-check-into-validate_page_before_insert.patch
mm-memory-cleanly-support-zeropage-in-vm_insert_page-vm_map_pages-and-vmf_insert_mixed.patch
mm-rmap-sanity-check-that-zeropages-are-not-passed-to-rmap.patch
mm-update-_mapcount-and-page_type-documentation.patch
mm-allow-reuse-of-the-lower-16-bit-of-the-page-type-with-an-actual-type.patch
mm-zsmalloc-use-a-proper-page-type.patch
mm-page_alloc-clear-pagebuddy-using-__clearpagebuddy-for-bad-pages.patch
mm-filemap-reinitialize-folio-_mapcount-directly.patch
mm-mm_init-initialize-page-_mapcount-directly-in-__init_single_page.patch
fs-proc-task_mmu-indicate-pm_file-for-pmd-mapped-file-thp.patch
fs-proc-task_mmu-dont-indicate-pm_mmap_exclusive-without-pm_present.patch
fs-proc-task_mmu-properly-detect-pm_mmap_exclusive-per-page-of-pmd-mapped-thps.patch
fs-proc-task_mmu-account-non-present-entries-as-maybe-shared-but-no-idea-how-often.patch
fs-proc-move-page_mapcount-to-fs-proc-internalh.patch
documentation-admin-guide-mm-pagemaprst-drop-using-pagemap-to-do-something-useful.patch
mm-pass-meminit_context-to-__free_pages_core.patch
mm-pass-meminit_context-to-__free_pages_core-fix.patch
mm-memory_hotplug-initialize-memmap-of-zone_device-with-pageoffline-instead-of-pagereserved.patch
mm-memory_hotplug-skip-adjust_managed_page_count-for-pageoffline-pages-when-offlining.patch
mm-highmem-reimplement-totalhigh_pages-by-walking-zones.patch
mm-highmem-make-nr_free_highpages-return-unsigned-long.patch
