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Tue, 10 Nov 2026 03:57:21 -0800 (PST) Received: from [10.125.112.22] ([122.11.210.25]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b16fea4243sm1639325a91.14.2026.11.10.03.57.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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 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