fs: add a filesystem flag for THPs

The page cache needs to know whether the filesystem supports THPs so that
it doesn't send THPs to filesystems which can't handle them.  Dave Chinner
points out that getting from the page mapping to the filesystem type is
too many steps (mapping->host->i_sb->s_type->fs_flags) so cache that
information in the address space flags.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Link: https://lkml.kernel.org/r/20200916032717.22917-1-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/inode.c b/fs/inode.c
index 72c4c34..9d78c37 100644 (file)
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -181,6 +181,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
        mapping->a_ops = &empty_aops;
        mapping->host = inode;
        mapping->flags = 0;
+       if (sb->s_type->fs_flags & FS_THP_SUPPORT)
+               __set_bit(AS_THP_SUPPORT, &mapping->flags);
        mapping->wb_err = 0;
        atomic_set(&mapping->i_mmap_writable, 0);
 #ifdef CONFIG_READ_ONLY_THP_FOR_FS

diff --git a/include/linux/fs.h b/include/linux/fs.h
index ae97d87..72369be 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2209,6 +2209,7 @@ struct file_system_type {
 #define FS_HAS_SUBTYPE         4
 #define FS_USERNS_MOUNT                8       /* Can be mounted by userns root */
 #define FS_DISALLOW_NOTIFY_PERM        16      /* Disable fanotify permission events */
+#define FS_THP_SUPPORT         8192    /* Remove once all fs converted */
 #define FS_RENAME_DOES_D_MOVE  32768   /* FS will handle d_move() during rename() internally. */
        int (*init_fs_context)(struct fs_context *);
        const struct fs_parameter_spec *parameters;

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c3afd32..820c970 100644 (file)
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -29,6 +29,7 @@ enum mapping_flags {
        AS_EXITING      = 4,    /* final truncate in progress */
        /* writeback related tags are not used */
        AS_NO_WRITEBACK_TAGS = 5,
+       AS_THP_SUPPORT = 6,     /* THPs supported */
 };
 
 /**
@@ -120,6 +121,11 @@ static inline void mapping_set_gfp_mask(struct address_space *m, gfp_t mask)
        m->gfp_mask = mask;
 }
 
+static inline bool mapping_thp_support(struct address_space *mapping)
+{
+       return test_bit(AS_THP_SUPPORT, &mapping->flags);
+}
+
 void release_pages(struct page **pages, int nr);
 
 /*

diff --git a/mm/shmem.c b/mm/shmem.c
index 6d4ddef..537c137 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3984,7 +3984,7 @@ static struct file_system_type shmem_fs_type = {
        .parameters     = shmem_fs_parameters,
 #endif
        .kill_sb        = kill_litter_super,
-       .fs_flags       = FS_USERNS_MOUNT,
+       .fs_flags       = FS_USERNS_MOUNT | FS_THP_SUPPORT,
 };
 
 int __init shmem_init(void)