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b=oKVTp6KAQCxqCCoKSLQzOOSP35j2OIp7iBzMm2hm2Pcd7chbFmWhl0eOFJn1ojRR2 as0eQmcmZk6Kc2mbV2yTAXZmd8qtl1UEfzZW6Eh9qh46HJFHrdscn7YkMXrnQfYb3A v4pfhjFDR/jKcOU+DbNbDLa/sLuA2AHQQ9z33yZ2oGHeGoTQvMKZ8ibkHX2smSkLU8 /7p0PnQvO2VDEbrRs9Zrgm8KfiSoPPZeGAHoMY29yewq0WiwYzY5GXLaksDcuPkMxd 1hhn8+VCJY4LnOYHQD3rrQ5uvl4G8IRXw2+NqfOS1ADvgPeRkHuL/CEsp5y39BMyam QWf1OkLYGZYdg== From: SeongJae Park To: Andrew Morton Cc: Josh Law , SeongJae Park , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2] mm/damon/core: document damos_commit_dests() failure semantics Date: Fri, 20 Mar 2026 07:36:45 -0700 Message-ID: <20260320143648.91673-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 56160A001C X-Rspamd-Server: rspam07 X-Stat-Signature: wy7nmp4gwbmhaz1ayy31xonktqa858r7 X-Rspam-User: X-HE-Tag: 1774017418-473507 X-HE-Meta: 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 quCZRrhg T+XdjMt9X1BsyROagxzUMq7eK/JyW6q8WBMIUHCJj2QdfcMYW/didP6wuSmEF8jXBaDKYNYEuaHmHUql5sXtcI+AGnsrpAdviyTUnsSv05VngviJzO2UV1XAI3TYP8iYS7BlE78VnGhQZsYws4QewYH60qtZV+gY6n0adsXG30VSxo32qTv6uZdp459q8Dr+DCu3x0NnfaXIdzMb3IKUxZFnw4os1gZKtQWOYLApnP1xOhHa+UHznsy7gqGgy6CaC+QU70s+PNBDoYfgqWGu4byr//pncrypnn32YIteuMRsk4Yt6W/xRPYG7CJqzOaScDVCzJzGftvKpp69aehFGMAUPrEmexdMje5OPUMg9LoFE6ervXt4Z6B1H24um2K9KlbfQvO7Knb3uqPzzSF0bF5DsuwLlzK2q2yrIjDj3U9KH9jg+YW6qgsRuEQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Josh Law Add a kernel-doc-like comment to damos_commit_dests() documenting its allocation failure contract: on -ENOMEM, the destination structure is left in a partially torn-down state that is safe to deallocate via damon_destroy_scheme(), but must not be reused for further commits. This was unclear from the code alone and led to a separate patch [1] attempting to reset nr_dests on failure. Make the intended usage explicit so future readers do not repeat the confusion. [1] https://lore.kernel.org/20260318214939.36100-1-objecting@objecting.org Signed-off-by: Josh Law Cc: Andrew Morton Reviewed-by: SeongJae Park Signed-off-by: SeongJae Park --- Changes from v1 (https://lore.kernel.org/20260319071332.114595-1-objecting@objecting.org) - Use kernel-doc like comment instead of kernel-doc for static function. - Add a link to the previous discussion. - Update description. - Rebase to latest mm-new. - Collect Reviewed-by: of SJ. mm/damon/core.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index 4dae03a37f9ac..df9f5e94e0ddd 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -1060,6 +1060,23 @@ static void damos_set_filters_default_reject(struct damos *s) damos_filters_default_reject(&s->ops_filters); } +/* + * damos_commit_dests() - Copy migration destinations from @src to @dst. + * @dst: Destination structure to update. + * @src: Source structure to copy from. + * + * If the number of destinations has changed, the old arrays in @dst are freed + * and new ones are allocated. On success, @dst contains a full copy of + * @src's arrays and count. + * + * On allocation failure, @dst is left in a partially torn-down state: its + * arrays may be NULL and @nr_dests may not reflect the actual allocation + * sizes. The structure remains safe to deallocate via damon_destroy_scheme(), + * but callers must not reuse @dst for further commits — it should be + * discarded. + * + * Return: 0 on success, -ENOMEM on allocation failure. + */ static int damos_commit_dests(struct damos_migrate_dests *dst, struct damos_migrate_dests *src) { base-commit: 4fbbbf18fd43c2d7b692749b7c853157f901b709 -- 2.47.3