On 28 Apr 2025, at 14:29, Nico Pache wrote:
setting /transparent_hugepages/enabled=always allows applications to benefit from THPs without having to madvise. However, the pf handler
s/pf/page fault
takes very few considerations to decide weather or not to actually use a
s/weather/whether
THP. This can lead to a lot of wasted memory. khugepaged only operates on memory that was either allocated with enabled=always or MADV_HUGEPAGE.
Introduce the ability to set enabled=defer, which will prevent THPs from being allocated by the page fault handler unless madvise is set, leaving it up to khugepaged to decide which allocations will collapse to a THP. This should allow applications to benefits from THPs, while curbing some of the memory waste.
Co-developed-by: Rafael Aquini raquini@redhat.com Signed-off-by: Rafael Aquini raquini@redhat.com Signed-off-by: Nico Pache npache@redhat.com
include/linux/huge_mm.h | 15 +++++++++++++-- mm/huge_memory.c | 31 +++++++++++++++++++++++++++---- 2 files changed, 40 insertions(+), 6 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index e3d15c737008..57e6c962afb1 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -48,6 +48,7 @@ enum transparent_hugepage_flag { TRANSPARENT_HUGEPAGE_UNSUPPORTED, TRANSPARENT_HUGEPAGE_FLAG, TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
- TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
What does INST mean here? Can you add one sentence on this new flag in the commit log to explain what it is short for?
TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG, @@ -186,6 +187,7 @@ static inline bool hugepage_global_enabled(void) { return transparent_hugepage_flags & ((1<<TRANSPARENT_HUGEPAGE_FLAG) |
(1<<TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG) | (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG));}
@@ -195,6 +197,12 @@ static inline bool hugepage_global_always(void) (1<<TRANSPARENT_HUGEPAGE_FLAG); }
+static inline bool hugepage_global_defer(void) +{
- return transparent_hugepage_flags &
(1<<TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG);+}
static inline int highest_order(unsigned long orders) { return fls_long(orders) - 1; @@ -291,13 +299,16 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma, unsigned long tva_flags, unsigned long orders) {
- if ((tva_flags & TVA_IN_PF) && hugepage_global_defer() &&
!(vm_flags & VM_HUGEPAGE))return 0;- /* Optimization to check if required orders are enabled early. */ if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) { unsigned long mask = READ_ONCE(huge_anon_orders_always);
This newline should stay, right?
The rest looks good to me. Thanks. Acked-by: Zi Yan ziy@nvidia.com
Best Regards, Yan, Zi