[PATCH v3 06/17] mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations

[Vlastimil Babka]

After the previous patch, we can distinguish costly allocations that should be
really lightweight, such as THP page faults, with __GFP_NORETRY. This means we
don't need to recognize khugepaged allocations via PF_KTHREAD anymore. We can
also change THP page faults in areas where madvise(MADV_HUGEPAGE) was used to
try as hard as khugepaged, as the process has indicated that it benefits from
THP's and is willing to pay some initial latency costs.

We can also make the flags handling less cryptic by distinguishing
GFP_TRANSHUGE_LIGHT (no reclaim at all, default mode in page fault) from
GFP_TRANSHUGE (only direct reclaim, khugepaged default). Adding __GFP_NORETRY
or __GFP_KSWAPD_RECLAIM is done where needed.

The patch effectively changes the current GFP_TRANSHUGE users as follows:

* get_huge_zero_page() - the zero page lifetime should be relatively long and
  it's shared by multiple users, so it's worth spending some effort on it.
  We use GFP_TRANSHUGE, and __GFP_NORETRY is not added. This also restores
  direct reclaim to this allocation, which was unintentionally removed by
  commit e4a49efe4e7e ("mm: thp: set THP defrag by default to madvise and add
  a stall-free defrag option")

* alloc_hugepage_khugepaged_gfpmask() - this is khugepaged, so latency is not
  an issue. So if khugepaged "defrag" is enabled (the default), do reclaim
  via GFP_TRANSHUGE without __GFP_NORETRY. We can remove the PF_KTHREAD check
  from page alloc.
  As a side-effect, khugepaged will now no longer check if the initial
  compaction was deferred or contended. This is OK, as khugepaged sleep times
  between collapsion attempts are long enough to prevent noticeable disruption,
  so we should allow it to spend some effort.

* migrate_misplaced_transhuge_page() - already was masking out __GFP_RECLAIM,
  so just convert to GFP_TRANSHUGE_LIGHT which is equivalent.

* alloc_hugepage_direct_gfpmask() - vma's with VM_HUGEPAGE (via madvise) are
  now allocating without __GFP_NORETRY. Other vma's keep using __GFP_NORETRY
  if direct reclaim/compaction is at all allowed (by default it's allowed only
  for madvised vma's). The rest is conversion to GFP_TRANSHUGE(_LIGHT).

[mhocko@xxxxxxxx: suggested GFP_TRANSHUGE_LIGHT]
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/gfp.h            | 14 ++++++++------
 include/trace/events/mmflags.h |  1 +
 mm/huge_memory.c               | 29 ++++++++++++++++-------------
 mm/khugepaged.c                |  2 +-
 mm/migrate.c                   |  2 +-
 mm/page_alloc.c                |  6 ++----
 tools/perf/builtin-kmem.c      |  1 +
 7 files changed, 30 insertions(+), 25 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index c29e9d347bc6..f8041f9de31e 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -237,9 +237,11 @@ struct vm_area_struct;
  *   are expected to be movable via page reclaim or page migration. Typically,
  *   pages on the LRU would also be allocated with GFP_HIGHUSER_MOVABLE.
  *
- * GFP_TRANSHUGE is used for THP allocations. They are compound allocations
- *   that will fail quickly if memory is not available and will not wake
- *   kswapd on failure.
+ * GFP_TRANSHUGE and GFP_TRANSHUGE_LIGHT are used for THP allocations. They are
+ *   compound allocations that will generally fail quickly if memory is not
+ *   available and will not wake kswapd/kcompactd on failure. The _LIGHT
+ *   version does not attempt reclaim/compaction at all and is by default used
+ *   in page fault path, while the non-light is used by khugepaged.
  */
 #define GFP_ATOMIC	(__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM)
 #define GFP_KERNEL	(__GFP_RECLAIM | __GFP_IO | __GFP_FS)
@@ -254,9 +256,9 @@ struct vm_area_struct;
 #define GFP_DMA32	__GFP_DMA32
 #define GFP_HIGHUSER	(GFP_USER | __GFP_HIGHMEM)
 #define GFP_HIGHUSER_MOVABLE	(GFP_HIGHUSER | __GFP_MOVABLE)
-#define GFP_TRANSHUGE	((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
-			 __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN) & \
-			 ~__GFP_RECLAIM)
+#define GFP_TRANSHUGE_LIGHT	((GFP_HIGHUSER_MOVABLE | __GFP_COMP | \
+			 __GFP_NOMEMALLOC | __GFP_NOWARN) & ~__GFP_RECLAIM)
+#define GFP_TRANSHUGE	(GFP_TRANSHUGE_LIGHT | __GFP_DIRECT_RECLAIM)
 
 /* Convert GFP flags to their corresponding migrate type */
 #define GFP_MOVABLE_MASK (__GFP_RECLAIMABLE|__GFP_MOVABLE)
diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
index 43cedbf0c759..5a81ab48a2fb 100644
--- a/include/trace/events/mmflags.h
+++ b/include/trace/events/mmflags.h
@@ -11,6 +11,7 @@
 
 #define __def_gfpflag_names						\
 	{(unsigned long)GFP_TRANSHUGE,		"GFP_TRANSHUGE"},	\
+	{(unsigned long)GFP_TRANSHUGE_LIGHT,	"GFP_TRANSHUGE_LIGHT"}, \
 	{(unsigned long)GFP_HIGHUSER_MOVABLE,	"GFP_HIGHUSER_MOVABLE"},\
 	{(unsigned long)GFP_HIGHUSER,		"GFP_HIGHUSER"},	\
 	{(unsigned long)GFP_USER,		"GFP_USER"},		\
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6eff8b123a88..4c89970ef1d8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -539,23 +539,26 @@ static int __do_huge_pmd_anonymous_page(struct fault_env *fe, struct page *page,
 }
 
 /*
- * If THP is set to always then directly reclaim/compact as necessary
- * If set to defer then do no reclaim and defer to khugepaged
+ * If THP defrag is set to always then directly reclaim/compact as necessary
+ * If set to defer then do only background reclaim/compact and defer to khugepaged
  * If set to madvise and the VMA is flagged then directly reclaim/compact
+ * When direct reclaim/compact is allowed, don't retry except for flagged VMA's
  */
 static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
 {
-	gfp_t reclaim_flags = 0;
-
-	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG, &transparent_hugepage_flags) &&
-	    (vma->vm_flags & VM_HUGEPAGE))
-		reclaim_flags = __GFP_DIRECT_RECLAIM;
-	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG, &transparent_hugepage_flags))
-		reclaim_flags = __GFP_KSWAPD_RECLAIM;
-	else if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
-		reclaim_flags = __GFP_DIRECT_RECLAIM;
-
-	return GFP_TRANSHUGE | reclaim_flags;
+	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 | (vma_madvised ? 0 : __GFP_NORETRY);
+
+	return GFP_TRANSHUGE_LIGHT;
 }
 
 /* Caller must hold page table lock. */
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 93d5f87c00d5..555d860b9543 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -694,7 +694,7 @@ static bool khugepaged_scan_abort(int nid)
 /* Defrag for khugepaged will enter direct reclaim/compaction if necessary */
 static inline gfp_t alloc_hugepage_khugepaged_gfpmask(void)
 {
-	return GFP_TRANSHUGE | (khugepaged_defrag() ? __GFP_DIRECT_RECLAIM : 0);
+	return khugepaged_defrag() ? GFP_TRANSHUGE : GFP_TRANSHUGE_LIGHT;
 }
 
 #ifdef CONFIG_NUMA
diff --git a/mm/migrate.c b/mm/migrate.c
index c7531ccf65f4..e3f933b08535 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1929,7 +1929,7 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
 		goto out_dropref;
 
 	new_page = alloc_pages_node(node,
-		(GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_RECLAIM,
+		(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
 		HPAGE_PMD_ORDER);
 	if (!new_page)
 		goto out_fail;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 246cba86b257..8ea9d1be54e9 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3625,11 +3625,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 			/*
 			 * Looks like reclaim/compaction is worth trying, but
 			 * sync compaction could be very expensive, so keep
-			 * using async compaction, unless it's khugepaged
-			 * trying to collapse.
+			 * using async compaction.
 			 */
-			if (!(current->flags & PF_KTHREAD))
-				migration_mode = MIGRATE_ASYNC;
+			migration_mode = MIGRATE_ASYNC;
 		}
 	}
 
diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c
index c9cb3be47cff..0d98182dc159 100644
--- a/tools/perf/builtin-kmem.c
+++ b/tools/perf/builtin-kmem.c
@@ -608,6 +608,7 @@ static const struct {
 	const char *compact;
 } gfp_compact_table[] = {
 	{ "GFP_TRANSHUGE",		"THP" },
+	{ "GFP_TRANSHUGE_LIGHT",	"THL" },
 	{ "GFP_HIGHUSER_MOVABLE",	"HUM" },
 	{ "GFP_HIGHUSER",		"HU" },
 	{ "GFP_USER",			"U" },
-- 
2.8.4