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Sun, 16 Aug 2026 18:46:58 -0400 (EDT) From: Kiryl Shutsemau To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, nico.pache@linux.dev Cc: baolin.wang@linux.alibaba.com, baohua@kernel.org, dev.jain@arm.com, hughd@google.com, lance.yang@linux.dev, liam@infradead.org, mhocko@suse.com, rppt@kernel.org, ryan.roberts@arm.com, shuah@kernel.org, surenb@google.com, usama.arif@linux.dev, vbabka@kernel.org, ziy@nvidia.com, usama.anjum@arm.com, agordeev@linux.ibm.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, kas@kernel.org, jannh@google.com, willy@infradead.org, pfalcato@suse.de, rostedt@goodmis.org, mhiramat@kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: [RFC PATCH 21/57] mm/collapse: settle whatever the round reached Date: Sun, 16 Aug 2026 23:45:33 +0100 Message-ID: <20260816224609.308019-22-kirill@shutemov.name> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260816224609.308019-1-kirill@shutemov.name> References: <20260816224609.308019-1-kirill@shutemov.name> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Kiryl Shutsemau (Meta)" Fill in the last pass. A candidate that never froze is recorded as given up on, with whatever result ended the round. Anything no pass took ownership of -- a destination folio, a table meant for deposit -- goes back. The count of installed candidates is what the round reports. Holding no lock here is the point. Every refusal before this happens under a page-table lock: the freeze unwinds under the ptl it took, and the install aborts under that ptl or the pmd lock. Dropping the last reference to a folio, and the memcg uncharge behind it, is not spinlock work. So a refused candidate keeps its folio and its table until the round is over, and this is where they are released. Assisted-by: Claude-Code:claude-opus-5 Signed-off-by: Kiryl Shutsemau (Meta) --- mm/collapse.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/mm/collapse.c b/mm/collapse.c index f65f413339bf..2da1f8ddcca8 100644 --- a/mm/collapse.c +++ b/mm/collapse.c @@ -1500,7 +1500,30 @@ static unsigned int collapse_finish(struct mm_struct *mm, struct collapse_control *cc, enum scan_result result) { - return 0; + unsigned int i, nr_installed = 0; + + for (i = 0; i < cc->nr_candidates; i++) { + struct collapse_candidate *cand = &cc->candidates[i]; + + /* Never froze: the round gave up before it got that far */ + if (cand->state == CAND_SELECTED) { + cand->state = CAND_SKIPPED; + cand->result = result; + } + + if (cand->new_folio) { + folio_put(cand->new_folio); + cand->new_folio = NULL; + } + if (cand->deposit) { + pte_free(mm, cand->deposit); + cand->deposit = NULL; + } + if (cand->state == CAND_INSTALLED) + nr_installed++; + } + + return nr_installed; } /* -- 2.54.0