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Tue, 10 Nov 2026 03:57:20 -0800 (PST) Message-ID: <8a7c7bff-2be9-438d-b8bb-e75361be56cf@gmail.com> Date: Tue, 10 Nov 2026 19:57:13 +0800 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/migrate: fix mlock state loss when migrating PTE-mapped large folios To: "David Hildenbrand (Arm)" , hughd@google.com, akpm@linux-foundation.org Cc: ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261109090846.1068409-1-chenwandun1@gmail.com> Content-Language: en-US From: Wandun In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: m3woby9p93fz55zyph4d7jz1yy8aozhc X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 03B8540002 X-Spam-Status: No, score=-14.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1794311842-806057 X-HE-Meta: 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 7KfNcpqt kryUf0Fz+8EbZj3Ao9zXQV1rP2FqAolyfSUQA/FgtTd+I4U9asTTEUi/N3sHSiIm9jOEzbX2ml1VS8gbLR9ojbVGHKsgT5FFMtWq8goVgWORG/BHGOAHtFMAKU+M9tES7+ZVjJ/A21+IJfXD4X0juZP/iILm1Ox3PnH9exDXZvFIeREbs/j5w1cjp9ZWyiS9pigjE6PPi2w8DbfzQIujS2kD+xTwRdtNJjO4OjCT/K+HV5SBEMeh68q2duYsx5CoYJc6wbFzWfyzC+x61emRTjW6ela3MQxWXWDPrBSU58RhPy+3eUSoHs/DU1ZouaMycviOdj660g+v6CeWKUe84pEnV3dWak3Z7d9iOF1Kz7waX57LbAjS8kJ6EnOU9GDXYy4IO+d26qx6M/WAeeWItK+pM3e6sX8bqTzLmjzZvlEwA4RKEWLw1WrOZ+XOGEcH+lhuRmsTPnrORUpHna5mLcf/QXCMFPlQzCLGKXPiCGYJ8qATjycqeZZhSYk7sjWnwieHfzxTvCmGmtYsU7k2x3YHuWb91D7K5sLuQhCltYvW1JOkbG0FRJ9n17jZHqHpUSv5Z Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 11/10/26 19:16, David Hildenbrand (Arm) wrote: > On 11/10/26 07:27, Wandun wrote: >> >> >> On 11/9/26 21:51, David Hildenbrand (Arm) wrote: >>> On 11/9/26 10:08, Wandun Chen wrote: >>>> From: Wandun Chen >>>> >>>> try_to_migrate() clears PG_mlocked when unmapping the source folio. >>>> For PTE-mapped large folios, remove_migration_pte() restores one PTE at >>>> a time, but the rmap helpers only restore mlock for full-folio mappings. >>>> This leaves the destination PTE-mapped large folio without PG_mlocked. >>>> >>>> Restore mlock once all PTEs of the destination folio are restored under >>>> a single page table lock. >>>> >>>> Fixes: dc68badcede4 ("mm: mlock: update mlock_pte_range to handle large folio") >>>> Signed-off-by: Wandun Chen >>>> --- >>>> mm/migrate.c | 10 +++++++++- >>>> 1 file changed, 9 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/mm/migrate.c b/mm/migrate.c >>>> index 94033c222e04..140e291d4587 100644 >>>> --- a/mm/migrate.c >>>> +++ b/mm/migrate.c >>>> @@ -353,6 +353,7 @@ static bool remove_migration_pte(struct folio *folio, >>>> { >>>> struct rmap_walk_arg *rmap_walk_arg = arg; >>>> DEFINE_FOLIO_VMA_WALK(pvmw, rmap_walk_arg->folio, vma, addr, PVMW_SYNC | PVMW_MIGRATION); >>>> + unsigned long nr_ptes = 0; >>>> >>>> while (page_vma_mapped_walk(&pvmw)) { >>>> rmap_t rmap_flags = RMAP_NONE; >>>> @@ -446,9 +447,16 @@ static bool remove_migration_pte(struct folio *folio, >>>> else >>>> folio_add_file_rmap_pte(folio, new, vma); >>>> set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte); >>>> + >>>> + nr_ptes++; >>>> } >>>> - if (READ_ONCE(vma->vm_flags) & VM_LOCKED) >>>> + if (READ_ONCE(vma->vm_flags) & VM_LOCKED) { >>>> + if (folio_test_large(folio) && >>>> + nr_ptes == folio_nr_pages(folio) && >>>> + !(pvmw.flags & PVMW_PGTABLE_CROSSED)) >>>> + mlock_vma_folio(folio, vma); >>>> mlock_drain_local(); >>>> + } >>> >>> I have the recollection that the next try_to_unmap() would fix that up? Or is >>> that not the case? >> >> It is the case, try_to_unmap() can restore it. However, until reclaim scans >> the folio, Mlocked in /proc/meminfo can remain undercounted, giving users >> a misleading impression that less memory is locked. >> >> A similar fix was made in commit >> ab521b4142aa ("mm/rmap: improve mlock tracking for large folios"). >> >> and handles cases where an entire folio is added in one rmap operation. >> >> However, when a PTE-mapped large folio is migrated, remove_migration_pte() >> restores PTEs individually, passing nr_pages = 1 to the rmap helpers, >> as a result, PG_mlocked is not set on the destination folio. >> >> This patch handles that case once the full mapping has been restored, >> rather than waiting for try_to_unmap() to restore the mlock state. > > Please revise the patch description pointing all that out :) Sure, I'll update the patch description in next version. > > Note that ab521b4142aa wasn't a fix (no Fixes:) why should this one here be one? > I also agree that the Fixes tag should be dropped. I was hesitant about including Fixes tag in v1, as there was no single obvious commit to reference. I eventually added it because I considered the Mlocked undercount in /proc/meminfo an accounting bug. Best regards, Wandun