exofs: Override read-ahead to align on stripe_size

* Set all inode->i_mapping->backing_dev_info to point to
  the per super-block sb->s_bdi.

* Calculating a read_ahead that is:
  - preferable 2 stripes long
    (Future patch will add a mount option to override this)
  - Minimum 128K aligned up to stripe-size
  - Caped to maximum-IO-sizes round down to stripe_size.
    (Max sizes are governed by max bio-size that fits in a page
     times number-of-devices)

CC: Marc Dionne <marc.c.dionne@gmail.com>
Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>

3 files changed, 35 insertions, 4 deletions

diff --git a/fs/exofs/exofs.h b/fs/exofs/exofs.h
index 2dc925fa1010..99fcb9126a97 100644
--- a/fs/exofs/exofs.h
+++ b/fs/exofs/exofs.h
@@ -256,6 +256,8 @@ static inline int exofs_oi_read(struct exofs_i_info *oi,
 }
 
 /* inode.c               */
+unsigned exofs_max_io_pages(struct exofs_layout *layout,
+                            unsigned expected_pages);
 int exofs_setattr(struct dentry *, struct iattr *);
 int exofs_write_begin(struct file *file, struct address_space *mapping,
                 loff_t pos, unsigned len, unsigned flags,
diff --git a/fs/exofs/inode.c b/fs/exofs/inode.c
index fb9d38056103..681b3cb9b4d8 100644
--- a/fs/exofs/inode.c
+++ b/fs/exofs/inode.c
@@ -43,6 +43,17 @@ enum { BIO_MAX_PAGES_KMALLOC =
                 PAGE_SIZE / sizeof(struct page *),
 };
 
+unsigned exofs_max_io_pages(struct exofs_layout *layout,
+                            unsigned expected_pages)
+{
+        unsigned pages = min_t(unsigned, expected_pages, MAX_PAGES_KMALLOC);
+
+        /* TODO: easily support bio chaining */
+        pages =  min_t(unsigned, pages,
+                       layout->group_width * BIO_MAX_PAGES_KMALLOC);
+        return pages;
+}
+
 struct page_collect {
         struct exofs_sb_info *sbi;
         struct inode *inode;
@@ -97,8 +108,7 @@ static void _pcol_reset(struct page_collect *pcol)
 
 static int pcol_try_alloc(struct page_collect *pcol)
 {
-        unsigned pages = min_t(unsigned, pcol->expected_pages,
-                          MAX_PAGES_KMALLOC);
+        unsigned pages;
 
         if (!pcol->ios) { /* First time allocate io_state */
                 int ret = exofs_get_io_state(&pcol->sbi->layout, &pcol->ios);
@@ -108,8 +118,7 @@ static int pcol_try_alloc(struct page_collect *pcol)
         }
 
         /* TODO: easily support bio chaining */
-        pages =  min_t(unsigned, pages,
-                       pcol->sbi->layout.group_width * BIO_MAX_PAGES_KMALLOC);
+        pages =  exofs_max_io_pages(&pcol->sbi->layout, pcol->expected_pages);
 
         for (; pages; pages >>= 1) {
                 pcol->pages = kmalloc(pages * sizeof(struct page *),
@@ -1049,6 +1058,7 @@ struct inode *exofs_iget(struct super_block *sb, unsigned long ino)
                 memcpy(oi->i_data, fcb.i_data, sizeof(fcb.i_data));
         }
 
+        inode->i_mapping->backing_dev_info = sb->s_bdi;
         if (S_ISREG(inode->i_mode)) {
                 inode->i_op = &exofs_file_inode_operations;
                 inode->i_fop = &exofs_file_operations;
@@ -1149,6 +1159,7 @@ struct inode *exofs_new_inode(struct inode *dir, int mode)
 
         sbi = sb->s_fs_info;
 
+        inode->i_mapping->backing_dev_info = sb->s_bdi;
         sb->s_dirt = 1;
         inode_init_owner(inode, dir, mode);
         inode->i_ino = sbi->s_nextid++;
diff --git a/fs/exofs/super.c b/fs/exofs/super.c
index 78f5ad633d3b..e87510f4749e 100644
--- a/fs/exofs/super.c
+++ b/fs/exofs/super.c
@@ -390,6 +390,23 @@ static int _read_and_match_data_map(struct exofs_sb_info *sbi, unsigned numdevs,
         return 0;
 }
 
+static unsigned __ra_pages(struct exofs_layout *layout)
+{
+        const unsigned _MIN_RA = 32; /* min 128K read-ahead */
+        unsigned ra_pages = layout->group_width * layout->stripe_unit /
+                                PAGE_SIZE;
+        unsigned max_io_pages = exofs_max_io_pages(layout, ~0);
+
+        ra_pages *= 2; /* two stripes */
+        if (ra_pages < _MIN_RA)
+                ra_pages = roundup(_MIN_RA, ra_pages / 2);
+
+        if (ra_pages > max_io_pages)
+                ra_pages = max_io_pages;
+
+        return ra_pages;
+}
+
 /* @odi is valid only as long as @fscb_dev is valid */
 static int exofs_devs_2_odi(struct exofs_dt_device_info *dt_dev,
                              struct osd_dev_info *odi)
@@ -623,6 +640,7 @@ static int exofs_fill_super(struct super_block *sb, void *data, int silent)
         }
 
         /* set up operation vectors */
+        sbi->bdi.ra_pages = __ra_pages(&sbi->layout);
         sb->s_bdi = &sbi->bdi;
         sb->s_fs_info = sbi;
         sb->s_op = &exofs_sops;