The patch titled Subject: mm: fix khugepaged activation policy has been added to the -mm mm-unstable branch. Its filename is mm-fix-khugepaged-activation-policy.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Ryan Roberts ryan.roberts@arm.com Subject: mm: fix khugepaged activation policy Date: Thu, 4 Jul 2024 10:10:50 +0100

Since the introduction of mTHP, the docuementation has stated that khugepaged would be enabled when any mTHP size is enabled, and disabled when all mTHP sizes are disabled. There are 2 problems with this; 1. this is not what was implemented by the code and 2. this is not the desirable behavior.

Desirable behavior is for khugepaged to be enabled when any PMD-sized THP is enabled, anon or file. (Note that file THP is still controlled by the top-level control so we must always consider that, as well as the PMD-size mTHP control for anon). khugepaged only supports collapsing to PMD-sized THP so there is no value in enabling it when PMD-sized THP is disabled. So let's change the code and documentation to reflect this policy.

Further, per-size enabled control modification events were not previously forwarded to khugepaged to give it an opportunity to start or stop. Consequently the following was resulting in khugepaged eroneously not being activated:

echo never > /sys/kernel/mm/transparent_hugepage/enabled echo always > /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/enabled

Link: https://lkml.kernel.org/r/20240704091051.2411934-1-ryan.roberts@arm.com Signed-off-by: Ryan Roberts ryan.roberts@arm.com Fixes: 3485b88390b0 ("mm: thp: introduce multi-size THP sysfs interface") Closes: https://lore.kernel.org/linux-mm/7a0bbe69-1e3d-4263-b206-da007791a5c4@redhat... Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Barry Song baohua@kernel.org Cc: David Hildenbrand david@redhat.com Cc: Jonathan Corbet corbet@lwn.net Cc: Lance Yang ioworker0@gmail.com Cc: Yang Shi shy828301@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

Documentation/admin-guide/mm/transhuge.rst | 11 +++++------ include/linux/huge_mm.h | 15 ++++++++------- mm/huge_memory.c | 7 +++++++ mm/khugepaged.c | 13 ++++++------- 4 files changed, 26 insertions(+), 20 deletions(-)

--- a/Documentation/admin-guide/mm/transhuge.rst~mm-fix-khugepaged-activation-policy +++ a/Documentation/admin-guide/mm/transhuge.rst @@ -202,12 +202,11 @@ PMD-mappable transparent hugepage::

cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size

-khugepaged will be automatically started when one or more hugepage -sizes are enabled (either by directly setting "always" or "madvise", -or by setting "inherit" while the top-level enabled is set to "always" -or "madvise"), and it'll be automatically shutdown when the last -hugepage size is disabled (either by directly setting "never", or by -setting "inherit" while the top-level enabled is set to "never"). +khugepaged will be automatically started when PMD-sized THP is enabled +(either of the per-size anon control or the top-level control are set +to "always" or "madvise"), and it'll be automatically shutdown when +PMD-sized THP is disabled (when both the per-size anon control and the +top-level control are "never")

Khugepaged controls ------------------- --- a/include/linux/huge_mm.h~mm-fix-khugepaged-activation-policy +++ a/include/linux/huge_mm.h @@ -128,16 +128,17 @@ static inline bool hugepage_global_alway (1<<TRANSPARENT_HUGEPAGE_FLAG); }

-static inline bool hugepage_flags_enabled(void) +static inline bool hugepage_pmd_enabled(void) { /* - * We cover both the anon and the file-backed case here; we must return - * true if globally enabled, even when all anon sizes are set to never. - * So we don't need to look at huge_anon_orders_inherit. + * We cover both the anon 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. */ - return hugepage_global_enabled() || - READ_ONCE(huge_anon_orders_always) || - READ_ONCE(huge_anon_orders_madvise); + return (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && hugepage_global_enabled()) || + test_bit(PMD_ORDER, &huge_anon_orders_always) || + test_bit(PMD_ORDER, &huge_anon_orders_madvise) || + (test_bit(PMD_ORDER, &huge_anon_orders_inherit) && hugepage_global_enabled()); }

static inline int highest_order(unsigned long orders) --- a/mm/huge_memory.c~mm-fix-khugepaged-activation-policy +++ a/mm/huge_memory.c @@ -502,6 +502,13 @@ static ssize_t thpsize_enabled_store(str } else ret = -EINVAL;

+ if (ret > 0) { + int err; + + err = start_stop_khugepaged(); + if (err) + ret = err; + } return ret; }

--- a/mm/khugepaged.c~mm-fix-khugepaged-activation-policy +++ a/mm/khugepaged.c @@ -449,7 +449,7 @@ void khugepaged_enter_vma(struct vm_area unsigned long vm_flags) { if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) && - hugepage_flags_enabled()) { + hugepage_pmd_enabled()) { if (thp_vma_allowable_order(vma, vm_flags, TVA_ENFORCE_SYSFS, PMD_ORDER)) __khugepaged_enter(vma->vm_mm); @@ -2462,8 +2462,7 @@ breakouterloop_mmap_lock:

static int khugepaged_has_work(void) { - return !list_empty(&khugepaged_scan.mm_head) && - hugepage_flags_enabled(); + return !list_empty(&khugepaged_scan.mm_head) && hugepage_pmd_enabled(); }

static int khugepaged_wait_event(void) @@ -2536,7 +2535,7 @@ static void khugepaged_wait_work(void) return; }

- if (hugepage_flags_enabled()) + if (hugepage_pmd_enabled()) wait_event_freezable(khugepaged_wait, khugepaged_wait_event()); }

@@ -2567,7 +2566,7 @@ static void set_recommended_min_free_kby int nr_zones = 0; unsigned long recommended_min;

- if (!hugepage_flags_enabled()) { + if (!hugepage_pmd_enabled()) { calculate_min_free_kbytes(); goto update_wmarks; } @@ -2617,7 +2616,7 @@ int start_stop_khugepaged(void) int err = 0;

mutex_lock(&khugepaged_mutex); - if (hugepage_flags_enabled()) { + if (hugepage_pmd_enabled()) { if (!khugepaged_thread) khugepaged_thread = kthread_run(khugepaged, NULL, "khugepaged"); @@ -2643,7 +2642,7 @@ fail: void khugepaged_min_free_kbytes_update(void) { mutex_lock(&khugepaged_mutex); - if (hugepage_flags_enabled() && khugepaged_thread) + if (hugepage_pmd_enabled() && khugepaged_thread) set_recommended_min_free_kbytes(); mutex_unlock(&khugepaged_mutex); } _

Patches currently in -mm which might be from ryan.roberts@arm.com are

mm-fix-khugepaged-activation-policy.patch