Please Help: 2.6.37 a_ops->readpages is never called, 2.6.36 was fine

115e19c53501edc11f730191f7f047736815ae3d is the first bad commit commit 115e19c53501edc11f730191f7f047736815ae3d
Author: Boaz Harrosh <Boaz Harrosh [email protected]>

    exofs: Set i_mapping->backing_dev_info anyway

OK It's stupid ME. But why please someone explain this issue? For now I'll send a revert, but I would like this explained, perhaps a more solid fix is needed.

commit: [115e19c] exofs: Set i_mapping->backing_dev_info anyway

Has caused a regression in read-ahead because bdi_init() does not set bdi->ra_pages to anything and it was left as zero. So when moving all inodes to point to the super-block's bdi, they all had ra_pages disabled.

Should bdi_init() be patched to some sane default value?

I fix that by calculating a read_ahead that is:
- preferable 2 stripes long (I'll add a mount option to next Kernel)
- 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 a page times

   # of devices)

This is a regression since the 2.6.37 Kernel.
2.6.36 was fine

CC Stable Tree <[email protected]>

Signed-off-by Boaz Harrosh <[email protected]>

---
 fs/exofs/exofs.h |    2 ++
 fs/exofs/inode.c |   17 +++++++++++++----
 fs/exofs/super.c |   18 ++++++++++++++++++
 3 files changed, 33 insertions(+), 4 deletions(-)

fs/exofs/exofs.h +2 -0

index 2dc925f..99fcb91 100644
@@ -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,

fs/exofs/inode.c +13 -4

index 4268542..deede10 100644
@@ -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 *),

fs/exofs/super.c +18 -0

index 79c3ae6..75d42ac 100644
@@ -383,6 +383,23 @@ 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)

@@ -616,6 +633,7 @@ 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;