[PATCH 05/14] mm/shmem: tweak the huge-page interface

[Matthew Auld]

In its current form huge-pages through shmemfs are controlled at the
super-block level, and are currently disabled by default, so to enable
huge-pages for a shmem backed gem object we would need to re-mount the
fs with the huge= argument, but for drm the mount is not user visible,
so good luck with that. The other option is the global sysfs knob
shmem_enabled which exposes the same huge= options, with the addition of
DENY and FORCE.

Neither option seems really workable, what we probably want is to able
to control the use of huge-pages at the time of pinning the backing
storage for a particular gem object, and only where it makes sense given
the size of the object. One caveat is when we write into the page cache
prior to pinning the backing storage. I played around with a bunch of
ideas but in the end just settled with driver overridable huge option
embedded in shmem_inode_info. Thoughts?

Signed-off-by: Matthew Auld <matthew.auld at intel.com>
---
 include/linux/shmem_fs.h | 1 +
 mm/shmem.c               | 9 ++++++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index a7d6bd2a918f..7dda18e74586 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -21,6 +21,7 @@ struct shmem_inode_info {
 	struct shared_policy	policy;		/* NUMA memory alloc policy */
 	struct simple_xattrs	xattrs;		/* list of xattrs */
 	struct inode		vfs_inode;
+	bool                    huge;           /* driver override sb_info.huge */
 };
 
 struct shmem_sb_info {
diff --git a/mm/shmem.c b/mm/shmem.c
index e67d6ba4e98e..98647cb34d06 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1727,6 +1727,9 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 			goto alloc_nohuge;
 		if (shmem_huge == SHMEM_HUGE_FORCE)
 			goto alloc_huge;
+		/* driver override kernel mounted sbinfo->huge */
+		if (info->huge)
+			goto alloc_huge;
 		switch (sbinfo->huge) {
 			loff_t i_size;
 			pgoff_t off;
@@ -2032,10 +2035,12 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 
 	if (shmem_huge != SHMEM_HUGE_FORCE) {
 		struct super_block *sb;
+		bool huge = false;
 
 		if (file) {
 			VM_BUG_ON(file->f_op != &shmem_file_operations);
 			sb = file_inode(file)->i_sb;
+			huge = SHMEM_I(file_inode(file))->huge;
 		} else {
 			/*
 			 * Called directly from mm/mmap.c, or drivers/char/mem.c
@@ -2045,7 +2050,7 @@ unsigned long shmem_get_unmapped_area(struct file *file,
 				return addr;
 			sb = shm_mnt->mnt_sb;
 		}
-		if (SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
+		if (!huge && SHMEM_SB(sb)->huge == SHMEM_HUGE_NEVER)
 			return addr;
 	}
 
@@ -4038,6 +4043,8 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
 		return true;
 	if (shmem_huge == SHMEM_HUGE_DENY)
 		return false;
+	if (SHMEM_I(inode)->huge)
+		return true;
 	switch (sbinfo->huge) {
 		case SHMEM_HUGE_NEVER:
 			return false;
-- 
2.9.3