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Howlett" , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH 7.2 v2 05/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check in hugepage_pmd_enabled() Date: Wed, 15 Apr 2026 14:01:27 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: <68F85F77-8EFE-449D-B643-AEEB38CB50B2@nvidia.com> In-Reply-To: <38697379-cbba-4c64-ae65-6774b01021d9@linux.alibaba.com> References: <20260413192030.3275825-1-ziy@nvidia.com> <20260413192030.3275825-6-ziy@nvidia.com> <05F00072-7E06-47C9-BC26-FE3736F557FC@nvidia.com> <84B8F641-A3DF-4219-AA57-6BA48E9B4998@nvidia.com> <998c02b6-2612-42c1-8099-d65ae275d1a2@kernel.org> <7468C68E-FB09-4714-94A3-4BED63453295@nvidia.com> <38697379-cbba-4c64-ae65-6774b01021d9@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8 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 g5RNhIBG Ah6RCnHF0Bshb7vy0eQ339IImPYn3WpxBT6652wu4CB1+hdrUPHH+/uPot1NlOEdEHLMQfHo2r5upqEwwwbUXFcVqE5pwB2N89+9nHgL2aPuOcIrE6oTHZ23S1mjvhyzXSyEZ6ZczGK0c9HuLJOP8wobUwjJI1kFQnqmIaHR88BQoVsWE8A/4eqRiAzAEK7jAgSs2iEPRY5vR06Mk9BMnn4OlZp0Lt6AfAtNZUYWYtUWsYY9Ia8YVyzRJgHV4gj7eDKnoZzVIhG5wGkg/4giHIGLTqGSLNm6cJIq0pVT4HSYE1JH5A+YF9sLUQ7U5TrNvga9l7kFUMrkjIugQ/gSGxl9rBY83DehCc/RfmUYcBexWBbw8KrVO/WL+1uaQsoRXddQCHx6yg2B1h+YagW/ueCIC/A8M80NTkzjpUUpY66+tfQlyhZvWOOaU26l//DlptFi1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 15 Apr 2026, at 5:21, Baolin Wang wrote: > On 4/15/26 4:00 PM, David Hildenbrand (Arm) wrote: >> On 4/15/26 08:36, Baolin Wang wrote: >>> >>> >>> On 4/15/26 2:25 AM, Zi Yan wrote: >>>> On 14 Apr 2026, at 14:14, David Hildenbrand (Arm) wrote: >>>> >>>>> >>>>> Yeah, it would be better if we could avoid it. But the dependency on = the >>>>> global toggle as it is today is a bit weird. >>>>> >>>>> >>>>> I don't think there is other interaction with FS and the global toggl= e >>>>> besides this and the one you are adjusting, right? >>>>> >>> >>> I'm afraid not. Please also consider the per-size mTHP interfaces. It's >>> possible that hugepage_global_enabled() returns false, but >>> hugepages-2048kB/enabled is set to "always", which would still allow >>> khugepaged to collapse folios. > > My comments are in reply to Zi=E2=80=99s comment: > > "I think hugepage_global_enabled() should be enough to decide whether khu= gepaged should run or not. " > > I=E2=80=99m concerned that only relying on hugepage_global_enabled() to d= ecide whether khugepaged should run would cause a regression for anonymous = and shmem memory collapse, as it ignores per-size mTHP configuration. > >> The question is really which semantics we want. >> >> Right now, there is no way to disable khugepaged for anon pages, to just >> get them during page faults. > > Right. > >> And we are now talking about the same problem for FS: to only get them >> during page faults (like we did so far without CONFIG_READ_ONLY_THP_FOR_= FS). > > OK. I=E2=80=99m fine with using hugepage_global_enabled() to determine wh= ether khugepaged scans file folios. > > My concern is that for anonymous memory and shmem, the per-size mTHP sett= ings should be considered. OK, I misunderstood the meaning of hugepage_global_enabled(), since per-siz= e mTHP settings could also enable khugepaged if PMD_SIZE is set. I will take willy=E2=80=99s original suggestion and make khugepaged on if t= he global setting is enabled. The below is the new version of this patch. I moved ano= n pmd huge page code to a separate anon_hpage_pmd_enabled() like shmem_hpage_pmd_enabled() and cleaned up the comment. Let me know your thou= ghts. Thanks. >From 92b92f2b2ab41c70b41dd304ce648786ee6a1603 Mon Sep 17 00:00:00 2001 From: Zi Yan Date: Wed, 15 Apr 2026 13:52:50 -0400 Subject: [PATCH] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check in hugepage_pmd_enabled() Remove READ_ONLY_THP_FOR_FS and khugepaged for file-backed pmd-sized hugepages are enabled by the global transparent hugepage control. khugepaged can still be enabled by per-size control for anon and shmem when the global control is off. Signed-off-by: Zi Yan --- mm/khugepaged.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index b8452dbdb043..586d27ce896e 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -406,18 +406,8 @@ static inline int collapse_test_exit_or_disable(struct= mm_struct *mm) mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm); } -static bool hugepage_pmd_enabled(void) +static inline bool anon_hpage_pmd_enabled() { - /* - * We cover the anon, shmem and the file-backed case here; file-backed - * hugepages, when configured in, are determined by the global control. - * Anon pmd-sized hugepages are determined by the pmd-size control. - * Shmem pmd-sized hugepages are also determined by its pmd-size control, - * except when the global shmem_huge is set to SHMEM_HUGE_DENY. - */ - if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && - hugepage_global_enabled()) - return true; if (test_bit(PMD_ORDER, &huge_anon_orders_always)) return true; if (test_bit(PMD_ORDER, &huge_anon_orders_madvise)) @@ -425,6 +415,20 @@ static bool hugepage_pmd_enabled(void) if (test_bit(PMD_ORDER, &huge_anon_orders_inherit) && hugepage_global_enabled()) return true; + return false; +} + +static bool hugepage_pmd_enabled(void) +{ + /* + * Anon, shmem and file-backed pmd-sized hugepages are all determined by + * the global control. If the global control is off, anon and shmem + * pmd-sized hugepages are also determined by its per-size control. + */ + if (hugepage_global_enabled()) + return true; + if (anon_hpage_pmd_enabled()) + return true; if (IS_ENABLED(CONFIG_SHMEM) && shmem_hpage_pmd_enabled()) return true; return false; --=20 2.43.0 Best Regards, Yan, Zi