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Mon, 20 Jul 2026 14:29:24 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id kOipN8QwXmrKTQAAD6G6ig (envelope-from ); Mon, 20 Jul 2026 14:29:24 +0000 From: Pedro Falcato To: Andrew Morton , David Hildenbrand , Lorenzo Stoakes Cc: Pedro Falcato , Zi Yan , Baolin Wang , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH 8/8] mm/khugepaged: fix and flesh out try_to_unmap_flush() comment Date: Mon, 20 Jul 2026 15:29:13 +0100 Message-ID: <20260720142913.846902-9-pfalcato@suse.de> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260720142913.846902-1-pfalcato@suse.de> References: <20260720142913.846902-1-pfalcato@suse.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Score: -6.80 X-Spamd-Result: default: False [-6.80 / 50.00]; REPLY(-4.00)[]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_MISSING_CHARSET(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-0.992]; MIME_GOOD(-0.10)[text/plain]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email,suse.de:mid]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_DN_SOME(0.00)[]; RCPT_COUNT_TWELVE(0.00)[15]; RCVD_VIA_SMTP_AUTH(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; R_RATELIMIT(0.00)[to_ip_from(RL8d8xedm6iu8o66torxsk6bwd)]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCVD_TLS_ALL(0.00)[] X-Spam-Level: Instead of vaguely handwaving that it should probably be done, flesh out any correctness concerns with try_to_unmap batching, flushing and its interaction with the rest of collapse_file(). Signed-off-by: Pedro Falcato --- mm/khugepaged.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index a09e4e4e1943..1999e094df20 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2560,15 +2560,19 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr, xa_unlocked: /* - * If collapse is successful, flush must be done now before copying. - * If collapse is unsuccessful, does flush actually need to be done? - * Do it anyway, to clear the state. + * try_to_unmap() flush must be done now before copying, regardless + * of success or not. In case of success, folios are about to be + * copied and collapsed onto a single large folio. In that case, + * stale TLB entries need to be flushed out, so no racing write may + * get lost. In case of failure, stale TLB entries need to be flushed + * out before putting the folio (which can possibly free it). */ try_to_unmap_flush(); if (result == SCAN_SUCCEED && nr_none && !shmem_charge(mapping->host, nr_none)) result = SCAN_FAIL; + if (result != SCAN_SUCCEED) { nr_none = 0; goto rollback; -- 2.55.0