+ mm-page_counter-constify-page_counter_read-and-page_counter_margin.patch added to mm-new branch

+ mm-page_counter-constify-page_counter_read-and-page_counter_margin.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm: page_counter: constify page_counter_read() and page_counter_margin()
has been added to the -mm mm-new branch.  Its filename is
     mm-page_counter-constify-page_counter_read-and-page_counter_margin.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_counter-constify-page_counter_read-and-page_counter_margin.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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

The -mm tree is included into linux-next via various
branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there most days

------------------------------------------------------
From: Tal Zussman <tz2294@columbia.edu>
Subject: mm: page_counter: constify page_counter_read() and page_counter_margin()
Date: Tue, 15 Sep 2026 19:20:10 -0400

Both only read the counter.  Constify them so that users can read counters
from const memcgs.

Link: https://lore.kernel.org/20260915-folio_memcg-const-v3-6-c239a6010b58@columbia.edu
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
---

 include/linux/page_counter.h |    4 ++--
 mm/page_counter.c            |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/include/linux/page_counter.h~mm-page_counter-constify-page_counter_read-and-page_counter_margin
+++ a/include/linux/page_counter.h
@@ -63,12 +63,12 @@ static inline void page_counter_init(str
 	counter->track_failcnt = false;
 }
 
-static inline unsigned long page_counter_read(struct page_counter *counter)
+static inline unsigned long page_counter_read(const struct page_counter *counter)
 {
 	return atomic_long_read(&counter->usage);
 }
 
-long page_counter_margin(struct page_counter *counter);
+long page_counter_margin(const struct page_counter *counter);
 void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages);
 void page_counter_charge(struct page_counter *counter, unsigned long nr_pages);
 bool page_counter_try_charge(struct page_counter *counter,
--- a/mm/page_counter.c~mm-page_counter-constify-page_counter_read-and-page_counter_margin
+++ a/mm/page_counter.c
@@ -54,7 +54,7 @@ static void propagate_protected_usage(st
  * Return: The minimum value of max minus usage across @counter and all of
  * its ancestors. The value may be negative during a concurrent charge.
  */
-long page_counter_margin(struct page_counter *counter)
+long page_counter_margin(const struct page_counter *counter)
 {
 	long margin = PAGE_COUNTER_MAX;
 
_

Patches currently in -mm which might be from tz2294@columbia.edu are

mm-page_io-convert-write-completion-handlers-to-folios.patch
mm-remove-pagereclaim.patch
mm-page_io-use-swap-entries-directly-in-zeromap-helpers.patch
mm-page_io-rename-bio_associate_blkg_from_page.patch
mm-page_io-refer-to-folios-in-swap_writeout-comments.patch
mm-swap-rename-__swap_writepage-to-__swap_writeout.patch
mm-remove-unused-mark_page_reserved.patch
mm-remove-unused-totalram_pages_inc-and-totalram_pages_dec.patch
mm-remove-pagewriteback.patch
mm-swap-add-folio_swap_entry-and-folio_page_swap_entry.patch
mm-swap-add-folio_swap_entry-and-folio_page_swap_entry-fix.patch
mm-huge_memory-add-a-comment-to-the-open-coded-swap-entry.patch
mm-rmap-use-folio_page_swap_entry-in-ttu_anon_swapbacked_folio.patch
mm-zswap-use-folio_swap_entry-in-zswap_store_page.patch
mm-swapfile-use-folio_page_swap_entry.patch
arm64-mte-make-mte_save_tags-and-mte_restore_tags-static.patch
arm64-mte-pass-the-swap-entry-to-mte_save_tags.patch
mm-swap-remove-page_swap_entry.patch
mm-memcontrol-take-a-const-folio-in-folio_memcg-and-friends.patch
mm-memcontrol-constify-obj_cgroup_memcg-and-friends.patch
mm-memcontrol-constify-the-lruvec-helpers.patch
mm-page_io-take-a-const-folio-in-bio_associate_blkg_from_folio.patch
mm-memcontrol-constify-the-mem_cgroup-accessors.patch
mm-page_counter-constify-page_counter_read-and-page_counter_margin.patch
mm-memcontrol-constify-the-reclaim-protection-helpers.patch
mm-memcontrol-constify-the-memcg-and-lruvec-stat-readers.patch
mm-memcontrol-constify-the-swap-accounting-helpers.patch
mm-memcontrol-constify-mem_cgroup_swappiness-and-mem_cgroup_get_max.patch
mm-memcontrol-constify-the-zswap-and-socket-pressure-helpers.patch