mm,thp,shmem: limit shmem THP alloc gfp_mask

Patch series "mm,thp,shm: limit shmem THP alloc gfp_mask", v6.

The allocation flags of anonymous transparent huge pages can be controlled
through the files in /sys/kernel/mm/transparent_hugepage/defrag, which can
help the system from getting bogged down in the page reclaim and
compaction code when many THPs are getting allocated simultaneously.

However, the gfp_mask for shmem THP allocations were not limited by those
configuration settings, and some workloads ended up with all CPUs stuck on
the LRU lock in the page reclaim code, trying to allocate dozens of THPs
simultaneously.

This patch applies the same configurated limitation of THPs to shmem
hugepage allocations, to prevent that from happening.

This way a THP defrag setting of "never" or "defer+madvise" will result in
quick allocation failures without direct reclaim when no 2MB free pages
are available.

With this patch applied, THP allocations for tmpfs will be a little more
aggressive than today for files mmapped with MADV_HUGEPAGE, and a little
less aggressive for files that are not mmapped or mapped without that
flag.

This patch (of 4):

The allocation flags of anonymous transparent huge pages can be controlled
through the files in /sys/kernel/mm/transparent_hugepage/defrag, which can
help the system from getting bogged down in the page reclaim and
compaction code when many THPs are getting allocated simultaneously.

However, the gfp_mask for shmem THP allocations were not limited by those
configuration settings, and some workloads ended up with all CPUs stuck on
the LRU lock in the page reclaim code, trying to allocate dozens of THPs
simultaneously.

This patch applies the same configurated limitation of THPs to shmem
hugepage allocations, to prevent that from happening.

Controlling the gfp_mask of THP allocations through the knobs in sysfs
allows users to determine the balance between how aggressively the system
tries to allocate THPs at fault time, and how much the application may end
up stalling attempting those allocations.

This way a THP defrag setting of "never" or "defer+madvise" will result in
quick allocation failures without direct reclaim when no 2MB free pages
are available.

With this patch applied, THP allocations for tmpfs will be a little more
aggressive than today for files mmapped with MADV_HUGEPAGE, and a little
less aggressive for files that are not mmapped or mapped without that
flag.

Link: https://lkml.kernel.org/r/20201124194925.623931-1-riel@surriel.com
Link: https://lkml.kernel.org/r/20201124194925.623931-2-riel@surriel.com
Signed-off-by: Rik van Riel <riel@surriel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Xu Yu <xuyu@linux.alibaba.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d77605c30f2e..395c75111d33 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -668,9 +668,9 @@ release:
  *	    available
  * never: never stall for any thp allocation
  */
-static inline gfp_t alloc_hugepage_direct_gfpmask(struct vm_area_struct *vma)
+gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma)
 {
-	const bool vma_madvised = !!(vma->vm_flags & VM_HUGEPAGE);
+	const bool vma_madvised = vma && (vma->vm_flags & VM_HUGEPAGE);
 
 	/* Always do synchronous compaction */
 	if (test_bit(TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG, &transparent_hugepage_flags))
@@ -762,7 +762,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 		}
 		return ret;
 	}
-	gfp = alloc_hugepage_direct_gfpmask(vma);
+	gfp = vma_thp_gfp_mask(vma);
 	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
 	if (unlikely(!page)) {
 		count_vm_event(THP_FAULT_FALLBACK);