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client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C Received: from satlexmb07.amd.com (165.204.84.17) by BN1PEPF0000467F.mail.protection.outlook.com (10.167.243.84) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.382.8 via Frontend Transport; Wed, 2 Sep 2026 10:53:24 +0000 Received: from [127.0.1.1] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.46; Wed, 2 Sep 2026 05:53:10 -0500 From: Shivank Garg Date: Wed, 2 Sep 2026 10:52:17 +0000 Subject: [PATCH RFC 03/11] mm/migrate: factor out folio splitting on allocation failure Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-ID: <20260902-migrate-refactor-shivank-v1-3-9dcca87669c4@amd.com> References: <20260902-migrate-refactor-shivank-v1-0-9dcca87669c4@amd.com> In-Reply-To: <20260902-migrate-refactor-shivank-v1-0-9dcca87669c4@amd.com> To: Andrew Morton , David Hildenbrand , Zi Yan , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , "Alistair Popple" , Vlastimil Babka , "Suren Baghdasaryan" , Michal Hocko , "Brendan Jackman" , Johannes Weiner , "SJ Park" , Jason Gunthorpe , John Hubbard , Peter Xu , Miaohe Lin , Naoya Horiguchi , "Oscar Salvador" , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Jan Kara , Jonathan Corbet , Shuah Khan , Randy Dunlap , "Alexander Viro" , Christian Brauner , Benjamin LaHaise , Chris Mason , David Sterba , Muchun Song , Dave Kleikamp , Trond Myklebust , Anna Schumaker , Mike Rapoport , Sean Christopherson , Paolo Bonzini , Bharata B Rao , David Rientjes , "Yiannis Nikolakopoulos" CC: , , , , , , , , , , , Shivank Garg X-Mailer: b4 0.15-dev-47d62 X-Developer-Signature: v=1; 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Factor this logic out into migrate_folio_split_on_alloc_fail() to simplify the allocation failure path. No functional change intended. Signed-off-by: Shivank Garg --- mm/migrate.c | 69 +++++++++++++++++++++++++++++++++++++----------------------- 1 file changed, 43 insertions(+), 26 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index 89207bf515b9..510dfffa7235 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1809,6 +1809,34 @@ static void migrate_folios_undo(struct list_head *src_folios, } } +static int migrate_folio_split_on_alloc_fail(struct folio *folio, + struct list_head *split_folios, enum migrate_mode mode, + enum migrate_reason reason, struct migrate_pages_stats *stats) +{ + bool is_thp = folio_test_pmd_mappable(folio); + int rc; + + /* Large folio NUMA faulting doesn't split to retry. */ + if (!folio_test_large(folio) || reason == MR_NUMA_MISPLACED) + return -ENOMEM; + + rc = try_split_folio(folio, split_folios, mode); + if (!rc) { + stats->nr_thp_split += is_thp; + stats->nr_split++; + return 0; + } + + /* + * Try again to split large folio to mitigate the failure of longterm + * pinning. + */ + if (reason == MR_LONGTERM_PIN && rc == -EAGAIN) + return -EAGAIN; + + return -ENOMEM; +} + /* * Unmap the folios in @from, queuing successfully unmapped sources on * @unmap_folios and their destination on @dst_folios. Increment @nr_failed for @@ -1829,10 +1857,8 @@ static int migrate_folios_unmap(struct list_head *from, int nr_retry_pages = 0; int pass = 0; bool is_thp = false; - bool is_large = false; struct folio *folio, *folio2, *dst = NULL; - int rc, nr_pages; - bool nosplit = (reason == MR_NUMA_MISPLACED); + int rc, split_rc, nr_pages; for (pass = 0; pass < nr_pass && retry; pass++) { retry = 0; @@ -1840,7 +1866,6 @@ static int migrate_folios_unmap(struct list_head *from, nr_retry_pages = 0; list_for_each_entry_safe(folio, folio2, from, lru) { - is_large = folio_test_large(folio); is_thp = folio_test_pmd_mappable(folio); nr_pages = folio_nr_pages(folio); @@ -1937,28 +1962,20 @@ static int migrate_folios_unmap(struct list_head *from, */ *nr_failed += 1; stats->nr_thp_failed += is_thp; - /* Large folio NUMA faulting doesn't split to retry. */ - if (is_large && !nosplit) { - int ret = try_split_folio(folio, split_folios, mode); - - if (!ret) { - stats->nr_thp_split += is_thp; - stats->nr_split++; - break; - } else if (reason == MR_LONGTERM_PIN && - ret == -EAGAIN) { - /* - * Try again to split large folio to - * mitigate the failure of longterm pinning. - */ - retry++; - thp_retry += is_thp; - nr_retry_pages += nr_pages; - /* Undo duplicated failure counting. */ - *nr_failed -= 1; - stats->nr_thp_failed -= is_thp; - break; - } + + split_rc = migrate_folio_split_on_alloc_fail(folio, + split_folios, mode, reason, stats); + if (!split_rc) + break; + /* Retry this folio in a later pass. */ + if (split_rc == -EAGAIN) { + retry++; + thp_retry += is_thp; + nr_retry_pages += nr_pages; + /* Undo duplicated failure counting. */ + *nr_failed -= 1; + stats->nr_thp_failed -= is_thp; + break; } stats->nr_failed_pages += nr_pages + nr_retry_pages; -- 2.43.0