On Fri, May 22, 2026 at 09:00:03AM -0600, Nico Pache wrote: > Add three new mTHP statistics to track collapse failures for different > orders when encountering swap PTEs, excessive none PTEs, and shared PTEs: > > - collapse_exceed_swap_pte: Increment when mTHP collapse fails due to > encountering a swap PTE. > > - collapse_exceed_none_pte: Counts when mTHP collapse fails due to > exceeding the none PTE threshold for the given order > > - collapse_exceed_shared_pte: Counts when mTHP collapse fails due to > encountering a shared PTE. > > These statistics complement the existing THP_SCAN_EXCEED_* events by > providing per-order granularity for mTHP collapse attempts. The stats are > exposed via sysfs under > `/sys/kernel/mm/transparent_hugepage/hugepages-*/stats/` for each > supported hugepage size. > > As we currently do not support collapsing mTHPs that contain a swap or > shared entry, those statistics keep track of how often we are > encountering failed mTHP collapses due to these restrictions. > > We will add support for mTHP collapse for anonymous pages next; lets also > track when this happens at the PMD level within the per-mTHP stats. > > Signed-off-by: Nico Pache <[email protected]>
Logic LGTM, small comment below, but otherwise: Reviewed-by: Lorenzo Stoakes <[email protected]> > --- > Documentation/admin-guide/mm/transhuge.rst | 14 ++++++++++++++ > include/linux/huge_mm.h | 3 +++ > mm/huge_memory.c | 7 +++++++ > mm/khugepaged.c | 21 +++++++++++++++++++-- > 4 files changed, 43 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/mm/transhuge.rst > b/Documentation/admin-guide/mm/transhuge.rst > index c51932e6275d..80a4d0bed70b 100644 > --- a/Documentation/admin-guide/mm/transhuge.rst > +++ b/Documentation/admin-guide/mm/transhuge.rst > @@ -714,6 +714,20 @@ nr_anon_partially_mapped > an anonymous THP as "partially mapped" and count it here, even though > it > is not actually partially mapped anymore. > > +collapse_exceed_none_pte > + The number of collapse attempts that failed due to exceeding the > + max_ptes_none threshold. > + > +collapse_exceed_swap_pte > + The number of collapse attempts that failed due to exceeding the > + max_ptes_swap threshold. For non-PMD orders this occurs if a mTHP > range > + contains at least one swap PTE. > + > +collapse_exceed_shared_pte > + The number of collapse attempts that failed due to exceeding the > + max_ptes_shared threshold. For non-PMD orders this occurs if a mTHP > range > + contains at least one shared PTE. > + > As the system ages, allocating huge pages may be expensive as the > system uses memory compaction to copy data around memory to free a > huge page for use. There are some counters in ``/proc/vmstat`` to help > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index ba7ae6808544..48496f09909b 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -144,6 +144,9 @@ enum mthp_stat_item { > MTHP_STAT_SPLIT_DEFERRED, > MTHP_STAT_NR_ANON, > MTHP_STAT_NR_ANON_PARTIALLY_MAPPED, > + MTHP_STAT_COLLAPSE_EXCEED_SWAP, > + MTHP_STAT_COLLAPSE_EXCEED_NONE, > + MTHP_STAT_COLLAPSE_EXCEED_SHARED, > __MTHP_STAT_COUNT > }; > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 345c54133c83..5c128cdec810 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -703,6 +703,10 @@ DEFINE_MTHP_STAT_ATTR(split_failed, > MTHP_STAT_SPLIT_FAILED); > DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED); > DEFINE_MTHP_STAT_ATTR(nr_anon, MTHP_STAT_NR_ANON); > DEFINE_MTHP_STAT_ATTR(nr_anon_partially_mapped, > MTHP_STAT_NR_ANON_PARTIALLY_MAPPED); > +DEFINE_MTHP_STAT_ATTR(collapse_exceed_swap_pte, > MTHP_STAT_COLLAPSE_EXCEED_SWAP); > +DEFINE_MTHP_STAT_ATTR(collapse_exceed_none_pte, > MTHP_STAT_COLLAPSE_EXCEED_NONE); > +DEFINE_MTHP_STAT_ATTR(collapse_exceed_shared_pte, > MTHP_STAT_COLLAPSE_EXCEED_SHARED); > + > > static struct attribute *anon_stats_attrs[] = { > &anon_fault_alloc_attr.attr, > @@ -719,6 +723,9 @@ static struct attribute *anon_stats_attrs[] = { > &split_deferred_attr.attr, > &nr_anon_attr.attr, > &nr_anon_partially_mapped_attr.attr, > + &collapse_exceed_swap_pte_attr.attr, > + &collapse_exceed_none_pte_attr.attr, > + &collapse_exceed_shared_pte_attr.attr, > NULL, > }; > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 928e32a0d4d7..fff6a8fbf1d4 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -649,7 +649,9 @@ static enum scan_result > __collapse_huge_page_isolate(struct vm_area_struct *vma, > if (pte_none_or_zero(pteval)) { > if (++none_or_zero > max_ptes_none) { > result = SCAN_EXCEED_NONE_PTE; > - count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > + if (is_pmd_order(order)) > + > count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > + count_mthp_stat(order, > MTHP_STAT_COLLAPSE_EXCEED_NONE); > goto out; > } > continue; > @@ -683,9 +685,17 @@ static enum scan_result > __collapse_huge_page_isolate(struct vm_area_struct *vma, > > /* See collapse_scan_pmd(). */ > if (folio_maybe_mapped_shared(folio)) { > + /* > + * TODO: Support shared pages without leading to further > + * mTHP collapses. Currently bringing in new pages via > + * shared may cause a future higher order collapse on a > + * rescan of the same range. > + */ Seems weird to add this comment in a stats update patch? Not a massively big deal but maybe worth moving to the relevant commit. > if (++shared > max_ptes_shared) { > result = SCAN_EXCEED_SHARED_PTE; > - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); > + if (is_pmd_order(order)) > + > count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); > + count_mthp_stat(order, > MTHP_STAT_COLLAPSE_EXCEED_SHARED); > goto out; > } > } > @@ -1138,6 +1148,7 @@ static enum scan_result > __collapse_huge_page_swapin(struct mm_struct *mm, > * range. > */ > if (!is_pmd_order(order)) { > + count_mthp_stat(order, MTHP_STAT_COLLAPSE_EXCEED_SWAP); > pte_unmap(pte); > mmap_read_unlock(mm); > result = SCAN_EXCEED_SWAP_PTE; > @@ -1433,6 +1444,8 @@ static enum scan_result collapse_scan_pmd(struct > mm_struct *mm, > if (++none_or_zero > max_ptes_none) { > result = SCAN_EXCEED_NONE_PTE; > count_vm_event(THP_SCAN_EXCEED_NONE_PTE); > + count_mthp_stat(HPAGE_PMD_ORDER, > + MTHP_STAT_COLLAPSE_EXCEED_NONE); > goto out_unmap; > } > continue; > @@ -1441,6 +1454,8 @@ static enum scan_result collapse_scan_pmd(struct > mm_struct *mm, > if (++unmapped > max_ptes_swap) { > result = SCAN_EXCEED_SWAP_PTE; > count_vm_event(THP_SCAN_EXCEED_SWAP_PTE); > + count_mthp_stat(HPAGE_PMD_ORDER, > + MTHP_STAT_COLLAPSE_EXCEED_SWAP); > goto out_unmap; > } > /* > @@ -1498,6 +1513,8 @@ static enum scan_result collapse_scan_pmd(struct > mm_struct *mm, > if (++shared > max_ptes_shared) { > result = SCAN_EXCEED_SHARED_PTE; > count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); > + count_mthp_stat(HPAGE_PMD_ORDER, > + > MTHP_STAT_COLLAPSE_EXCEED_SHARED); > goto out_unmap; > } > } > -- > 2.54.0 >
