mm,thp,shm: limit gfp mask to no more than specified

Matthew Wilcox pointed out that the i915 driver opportunistically
allocates tmpfs memory, but will happily reclaim some of its pool if no
memory is available.

Make sure the gfp mask used to opportunistically allocate a THP is always
at least as restrictive as the original gfp mask.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Rik van Riel <[email protected]>
Suggested-by: Matthew Wilcox <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xu Yu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 21 insertions, 0 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 596009a44431..06c771d23127 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1505,6 +1505,26 @@ static struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
 	return page;
 }
 
+/*
+ * Make sure huge_gfp is always more limited than limit_gfp.
+ * Some of the flags set permissions, while others set limitations.
+ */
+static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
+{
+	gfp_t allowflags = __GFP_IO | __GFP_FS | __GFP_RECLAIM;
+	gfp_t denyflags = __GFP_NOWARN | __GFP_NORETRY;
+	gfp_t result = huge_gfp & ~allowflags;
+
+	/*
+	 * Minimize the result gfp by taking the union with the deny flags,
+	 * and the intersection of the allow flags.
+	 */
+	result |= (limit_gfp & denyflags);
+	result |= (huge_gfp & limit_gfp) & allowflags;
+
+	return result;
+}
+
 static struct page *shmem_alloc_hugepage(gfp_t gfp,
 		struct shmem_inode_info *info, pgoff_t index)
 {
@@ -1864,6 +1884,7 @@ repeat:
 
 alloc_huge:
 	huge_gfp = vma_thp_gfp_mask(vma);
+	huge_gfp = limit_gfp_mask(huge_gfp, gfp);
 	page = shmem_alloc_and_acct_page(huge_gfp, inode, index, true);
 	if (IS_ERR(page)) {
 alloc_nohuge: