[PATCH AUTOSEL 7.0-6.6] docs: cgroup-v1: Update charge-commit section

[Sasha Levin <sashal@kernel.org>]

From: "T.J. Mercier" <tjmercier@google.com>

[ Upstream commit d8769544bde51b0ac980d10f8fe9f9fed6c95995 ]

Commit 1d8f136a421f ("memcg/hugetlb: remove memcg hugetlb
try-commit-cancel protocol") removed mem_cgroup_commit_charge() and
mem_cgroup_cancel_charge(), but the docs still refer to those functions.
There is no longer any charge cancellation.

Update the docs to match the code.

Signed-off-by: T.J. Mercier <tjmercier@google.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

## Phase 1: Commit Message Forensics
Step 1.1 Record: subsystem `docs: cgroup-v1`; action verb `Update`;
intent: update `Documentation/admin-guide/cgroup-v1/memcg_test.rst` so
the charge-commit section matches current memcg code.

Step 1.2 Record: tags present: `Signed-off-by: T.J. Mercier
<tjmercier@google.com>` and `Signed-off-by: Tejun Heo <tj@kernel.org>`.
No `Fixes:`, `Reported-by:`, `Tested-by:`, `Reviewed-by:`, `Acked-by:`,
`Link:`, or `Cc: stable@vger.kernel.org` tags in the committed message.

Step 1.3 Record: the body says commit `1d8f136a421f` removed
`mem_cgroup_commit_charge()` and `mem_cgroup_cancel_charge()`, while the
cgroup-v1 memcg docs still name them and describe cancellation.
Symptom/failure mode: incorrect documentation only. Version information:
the referenced removal commit is from 2025-01-13 in the local object
database; candidate commit is from 2026-04-30. Root cause: docs were not
updated when the code was changed.

Step 1.4 Record: this is not a hidden runtime bug fix. It is an explicit
documentation correctness fix.

## Phase 2: Diff Analysis
Step 2.1 Record: one file changed: `Documentation/admin-
guide/cgroup-v1/memcg_test.rst`, `2 insertions(+), 4 deletions(-)`. No
functions modified. Scope: single-file documentation-only surgical
change.

Step 2.2 Record: before, the section was titled `charge-commit-cancel`,
listed `mem_cgroup_commit_charge()` or `mem_cgroup_cancel_charge()`, and
described `cancel()`. After, it is titled `charge-commit`, lists
`commit_charge()`, and removes the cancellation text.

Step 2.3 Record: bug category is documentation/comment correctness.
Specific mechanism: removes stale references to APIs that are absent in
current `6.19.y`/`7.0.y` code and in `origin/master`.

Step 2.4 Record: fix quality is obviously correct for trees whose memcg
code no longer has `mem_cgroup_commit_charge()` /
`mem_cgroup_cancel_charge()`. Regression risk is zero runtime risk, but
there is a branch-selection concern: `stable/linux-6.12.y` still
contains those functions, so this exact doc update would be misleading
there.

## Phase 3: Git History Investigation
Step 3.1 Record: `git blame` before the candidate shows the stale doc
lines came from `f3f5edc5e41e` in this repository’s history. `git blame
origin/master` shows the changed lines attributed to `d8769544bde51`.

Step 3.2 Record: no `Fixes:` tag. I still inspected referenced commit
`1d8f136a421f26747e58c01281cba5bffae8d289`; it removed prototypes and
implementations for `mem_cgroup_commit_charge()`,
`mem_cgroup_cancel_charge()`, and related hugetlb try/commit/cancel
helpers.

Step 3.3 Record: recent history for `Documentation/admin-
guide/cgroup-v1/memcg_test.rst` on `origin/master` has only the file
introduction/import commit and this candidate. Related path history
shows the candidate was merged via `cgroup-for-7.1-rc2-fixes`. No
prerequisite doc series found.

Step 3.4 Record: author `T.J. Mercier` has at least one other cgroup-
related commit in `origin/master`; Tejun Heo is listed in `MAINTAINERS`
as cgroup maintainer and committed the patch.

Step 3.5 Record: no code dependencies for the patch itself. It can apply
standalone to the current `stable/linux-7.0.y` checkout. Applicability
must be gated by whether the target tree’s code has removed the old
APIs.

## Phase 4: Mailing List And External Research
Step 4.1 Record: `b4 dig -c d8769544bde51...` found the original
submission at
`https://patch.msgid.link/20260430201142.240387-1-tjmercier@google.com`.
`b4 dig -a` found only v1 of a single-patch series. The mbox contains
Tejun’s reply: “Applied to cgroup/for-7.1-fixes.” No NAKs or concerns
found in the saved thread.

Step 4.2 Record: `b4 dig -w` shows recipients included cgroup
maintainers/list and docs list: `tj@kernel.org`, `hannes@cmpxchg.org`,
`mkoutny@suse.com`, `cgroups@vger.kernel.org`, `corbet@lwn.net`,
`skhan@linuxfoundation.org`, `linux-doc@vger.kernel.org`, `linux-
kernel@vger.kernel.org`.

Step 4.3 Record: no `Reported-by` or bug-report `Link:` tags. No syzbot,
bugzilla, or user-impact bug report applies.

Step 4.4 Record: b4 found a standalone single-patch series, not part of
a multi-patch dependency chain.

Step 4.5 Record: web search did not find stable-list discussion for this
exact patch. `WebFetch` to lore/patch.msgid was blocked by Anubis, but
b4 successfully fetched the mbox.

## Phase 5: Code Semantic Analysis
Step 5.1 Record: no functions modified by the diff.

Step 5.2 Record: no callers affected by the diff. For documentation
accuracy, I verified current `stable/linux-7.0.y` code has
`commit_charge()` callers in `charge_memcg()`,
`mem_cgroup_replace_folio()`, and `mem_cgroup_migrate()`.

Step 5.3 Record: no changed callees. The relevant current code has
`commit_charge()` assigning `folio->memcg_data`, and callers also invoke
`memcg1_commit_charge()` where appropriate.

Step 5.4 Record: runtime reachability is not relevant because no
executable code changes.

Step 5.5 Record: similar stale docs pattern exists in stable branches;
however code state differs by branch. `6.19.y`/`7.0.y` have stale docs
and no old API. `6.12.y` still has `mem_cgroup_commit_charge()` and
`mem_cgroup_cancel_charge()` in code.

## Phase 6: Cross-Referencing And Stable Tree Analysis
Step 6.1 Record: buggy stale documentation exists in
`stable/linux-7.0.y`, `stable/linux-6.19.y`, `stable/linux-6.18.y`,
`stable/linux-6.6.y`, `stable/linux-6.1.y`, `stable/linux-5.15.y`, and
`stable/linux-5.10.y` by exact doc grep. I verified the old APIs are
absent in several of those trees, but `stable/linux-6.12.y` still
contains `mem_cgroup_commit_charge()` and `mem_cgroup_cancel_charge()`,
so this exact upstream text is not universally correct for all
maintained stable lines.

Step 6.2 Record: `git apply --check` of the candidate diff succeeds on
the current `stable/linux-7.0.y` checkout. Expected backport difficulty:
clean for trees with matching doc context; branch-specific review needed
for `6.12.y`.

Step 6.3 Record: no related stable fix for this exact doc update found
by local stable branch ancestry checks or web search.

## Phase 7: Subsystem And Maintainer Context
Step 7.1 Record: subsystem is cgroup-v1 memcg documentation.
Criticality: peripheral/runtime-none; important only for documentation
correctness.

Step 7.2 Record: cgroup and memcg areas are active; recent
`origin/master` history includes multiple cgroup/mm fixes. The candidate
was applied by the cgroup maintainer.

## Phase 8: Impact And Risk Assessment
Step 8.1 Record: affected population is documentation readers and
developers/admins consulting old cgroup-v1 memcg internals. No kernel
runtime users are affected.

Step 8.2 Record: trigger condition is reading or relying on the stale
documentation. Unprivileged users cannot trigger a kernel failure
because there is no runtime behavior.

Step 8.3 Record: failure mode is incorrect documentation. Severity: LOW.
It can mislead developers/admins, but it does not fix crash, corruption,
leak, deadlock, or security behavior.

Step 8.4 Record: benefit is low but real for documentation correctness,
especially because the stable rules exception allows
documentation/comment fixes and runtime risk is zero. Risk is very low
for branches whose code matches the new text; risk is documentation-
regression risk if applied to a branch like `6.12.y` where cancellation
APIs still exist.

## Phase 9: Final Synthesis
Step 9.1 Record: evidence for backporting: tiny docs-only patch;
corrects verified stale references in current `7.0.y` and `6.19.y`;
applied by cgroup maintainer; no runtime regression risk; documentation
fixes are allowed. Evidence against: no runtime bug or user-visible
stability issue; not correct for every stable branch, specifically
verified `6.12.y` still has the old commit/cancel APIs. Unresolved: I
did not exhaustively validate every maintained stable branch’s memcg API
state.

Step 9.2 Stable rules checklist:
1. Obviously correct and tested? Yes for matching-code branches;
   verified by code grep, `git diff --check`, and `git apply --check` on
   `7.0.y`.
2. Fixes a real bug that affects users? It fixes incorrect
   documentation, not runtime behavior.
3. Important issue? No runtime severity; LOW documentation correctness
   issue.
4. Small and contained? Yes, 6-line docs-only diff in one file.
5. No new features or APIs? Yes.
6. Can apply to stable trees? Yes to at least current `7.0.y`; should
   not be applied blindly to `6.12.y`.

Step 9.3 Record: exception category is documentation fix.

Step 9.4 Decision: backport is acceptable for stable trees whose memcg
implementation no longer has charge cancellation APIs. It should be
excluded from trees like `6.12.y` where the old APIs still exist. With
that branch-selection caveat, this qualifies under the documentation-fix
exception.

Verification:
- [Phase 1] Parsed candidate commit
  `d8769544bde51b0ac980d10f8fe9f9fed6c95995`: only two Signed-off-by
  tags, no bug/report/stable tags.
- [Phase 2] `git show --stat --patch`: confirmed one docs file, `2
  insertions(+), 4 deletions(-)`.
- [Phase 3] `git show 1d8f136a421f...`: confirmed referenced commit
  removed `mem_cgroup_commit_charge()` and `mem_cgroup_cancel_charge()`
  from mainline code.
- [Phase 3] `git log origin/master --grep`: found candidate and merge
  via `cgroup-for-7.1-rc2-fixes`.
- [Phase 4] `b4 dig`: found lore thread and exact patch-id match.
- [Phase 4] `b4 dig -a`: only v1 single-patch series.
- [Phase 4] `b4 dig -w`: relevant cgroup and docs maintainers/lists were
  included.
- [Phase 4] Saved mbox: confirmed Tejun replied “Applied to
  cgroup/for-7.1-fixes”; no NAKs or stable nomination found.
- [Phase 5] `rg`/`git grep`: confirmed current code uses
  `commit_charge()` and no longer has old API names in `7.0.y`.
- [Phase 6] `git apply --check`: candidate applies cleanly to current
  `7.0.y`.
- [Phase 6] Branch checks: `6.12.y` still has
  `mem_cgroup_commit_charge()` and `mem_cgroup_cancel_charge()`, so this
  patch must not be applied there unchanged.
- [Phase 8] Runtime impact verified as none because only
  `Documentation/admin-guide/cgroup-v1/memcg_test.rst` changes.

**YES**

 Documentation/admin-guide/cgroup-v1/memcg_test.rst | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v1/memcg_test.rst b/Documentation/admin-guide/cgroup-v1/memcg_test.rst
index 9f8e27355cba5..7c7cd457cf695 100644
--- a/Documentation/admin-guide/cgroup-v1/memcg_test.rst
+++ b/Documentation/admin-guide/cgroup-v1/memcg_test.rst
@@ -47,21 +47,19 @@ Please note that implementation details can be changed.
 	  Called when swp_entry's refcnt goes down to 0. A charge against swap
 	  disappears.
 
-3. charge-commit-cancel
+3. charge-commit
 =======================
 
 	Memcg pages are charged in two steps:
 
 		- mem_cgroup_try_charge()
-		- mem_cgroup_commit_charge() or mem_cgroup_cancel_charge()
+		- commit_charge()
 
 	At try_charge(), there are no flags to say "this page is charged".
 	at this point, usage += PAGE_SIZE.
 
 	At commit(), the page is associated with the memcg.
 
-	At cancel(), simply usage -= PAGE_SIZE.
-
 Under below explanation, we assume CONFIG_SWAP=y.
 
 4. Anonymous
-- 
2.53.0