mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations

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@suse.com: suggested GFP_TRANSHUGE_LIGHT]
Link: http://lkml.kernel.org/r/20160721073614.24395-7-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 13 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8f0cd35..2373f0a 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. */