Currently, when defrag is set to "madvise", thp allocations will direct
reclaim. However, when defrag is set to "defer", all thp allocations do
not attempt reclaim regardless of MADV_HUGEPAGE.
This patch always directly reclaims for MADV_HUGEPAGE regions when defrag
is not set to "never." The idea is that MADV_HUGEPAGE regions really
want to be backed by hugepages and are willing to endure the latency at
fault as it was the default behavior prior to commit 444eb2a449ef ("mm:
thp: set THP defrag by default to madvise and add a stall-free defrag
option").
In this form, "defer" is a stronger, more heavyweight version of
"madvise".
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
Documentation/vm/transhuge.txt | 7 +++++--
mm/huge_memory.c | 10 ++++++----
2 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
--- a/Documentation/vm/transhuge.txt
+++ b/Documentation/vm/transhuge.txt
@@ -121,8 +121,11 @@ to utilise them.
"defer" means that an application will wake kswapd in the background
to reclaim pages and wake kcompact to compact memory so that THP is
-available in the near future. It's the responsibility of khugepaged
-to then install the THP pages later.
+available in the near future, unless it is for a region where
+madvise(MADV_HUGEPAGE) has been used, in which case direct reclaim will be
+used. Kcompactd will attempt to make hugepages available for allocation in
+the near future and khugepaged will try to collapse existing memory into
+hugepages later.
"madvise" will enter direct reclaim like "always" but only for regions
that are have used madvise(MADV_HUGEPAGE). This is the default behaviour.
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -619,15 +619,17 @@ static int __do_huge_pmd_anonymous_page(struct vm_fault *vmf, struct page *page,
*/
static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
{
- bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
+ const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
&transparent_hugepage_flags) && vma_madvised)
return GFP_TRANSHUGE;
else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
- &transparent_hugepage_flags))
- return GFP_TRANSHUGE_LIGHT | __GFP_KSWAPD_RECLAIM;
- else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
+ &transparent_hugepage_flags)) {
+ return GFP_TRANSHUGE_LIGHT |
+ (vma_madvised ? __GFP_DIRECT_RECLAIM :
+ __GFP_KSWAPD_RECLAIM);
+ } else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
&transparent_hugepage_flags))
return GFP_TRANSHUGE | (vma_madvised ? 0 : __GFP_NORETRY);
--
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