1 files changed, 55 insertions, 34 deletions

diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index b0d264e684fd..f6a714c5aab0 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -16,12 +16,19 @@
 #include <linux/slab.h>
 #include <linux/dm-io.h>
 
+#define DM_MSG_PREFIX "io"
+
+#define DM_IO_MAX_REGIONS       BITS_PER_LONG
+
 struct dm_io_client {
         mempool_t *pool;
         struct bio_set *bios;
 };
 
-/* FIXME: can we shrink this ? */
+/*
+ * Aligning 'struct io' reduces the number of bits required to store
+ * its address.  Refer to store_io_and_region_in_bio() below.
+ */
 struct io {
         unsigned long error_bits;
         unsigned long eopnotsupp_bits;
@@ -30,7 +37,7 @@ struct io {
         struct dm_io_client *client;
         io_notify_fn callback;
         void *context;
-};
+} __attribute__((aligned(DM_IO_MAX_REGIONS)));
 
 static struct kmem_cache *_dm_io_cache;
 
@@ -92,18 +99,29 @@ EXPORT_SYMBOL(dm_io_client_destroy);
 
 /*-----------------------------------------------------------------
  * We need to keep track of which region a bio is doing io for.
- * In order to save a memory allocation we store this the last
- * bvec which we know is unused (blech).
- * XXX This is ugly and can OOPS with some configs... find another way.
+ * To avoid a memory allocation to store just 5 or 6 bits, we
+ * ensure the 'struct io' pointer is aligned so enough low bits are
+ * always zero and then combine it with the region number directly in
+ * bi_private.
  *---------------------------------------------------------------*/
-static inline void bio_set_region(struct bio *bio, unsigned region)
+static void store_io_and_region_in_bio(struct bio *bio, struct io *io,
+                                       unsigned region)
 {
-        bio->bi_io_vec[bio->bi_max_vecs].bv_len = region;
+        if (unlikely(!IS_ALIGNED((unsigned long)io, DM_IO_MAX_REGIONS))) {
+                DMCRIT("Unaligned struct io pointer %p", io);
+                BUG();
+        }
+
+        bio->bi_private = (void *)((unsigned long)io | region);
 }
 
-static inline unsigned bio_get_region(struct bio *bio)
+static void retrieve_io_and_region_from_bio(struct bio *bio, struct io **io,
+                                       unsigned *region)
 {
-        return bio->bi_io_vec[bio->bi_max_vecs].bv_len;
+        unsigned long val = (unsigned long)bio->bi_private;
+
+        *io = (void *)(val & -(unsigned long)DM_IO_MAX_REGIONS);
+        *region = val & (DM_IO_MAX_REGIONS - 1);
 }
 
 /*-----------------------------------------------------------------
@@ -144,10 +162,8 @@ static void endio(struct bio *bio, int error)
         /*
          * The bio destructor in bio_put() may use the io object.
          */
-        io = bio->bi_private;
-        region = bio_get_region(bio);
+        retrieve_io_and_region_from_bio(bio, &io, &region);
 
-        bio->bi_max_vecs++;
         bio_put(bio);
 
         dec_count(io, region, error);
@@ -247,7 +263,10 @@ static void vm_dp_init(struct dpages *dp, void *data)
 
 static void dm_bio_destructor(struct bio *bio)
 {
-        struct io *io = bio->bi_private;
+        unsigned region;
+        struct io *io;
+
+        retrieve_io_and_region_from_bio(bio, &io, &region);
 
         bio_free(bio, io->client->bios);
 }
@@ -292,24 +311,17 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
 
         while (remaining) {
                 /*
-                 * Allocate a suitably sized-bio: we add an extra
-                 * bvec for bio_get/set_region() and decrement bi_max_vecs
-                 * to hide it from bio_add_page().
+                 * Allocate a suitably sized-bio.
                  */
                 num_bvecs = dm_sector_div_up(remaining,
                                              (PAGE_SIZE >> SECTOR_SHIFT));
-                num_bvecs = 1 + min_t(int, bio_get_nr_vecs(where->bdev),
-                                      num_bvecs);
-                if (unlikely(num_bvecs > BIO_MAX_PAGES))
-                        num_bvecs = BIO_MAX_PAGES;
+                num_bvecs = min_t(int, bio_get_nr_vecs(where->bdev), num_bvecs);
                 bio = bio_alloc_bioset(GFP_NOIO, num_bvecs, io->client->bios);
                 bio->bi_sector = where->sector + (where->count - remaining);
                 bio->bi_bdev = where->bdev;
                 bio->bi_end_io = endio;
-                bio->bi_private = io;
                 bio->bi_destructor = dm_bio_destructor;
-                bio->bi_max_vecs--;
-                bio_set_region(bio, region);
+                store_io_and_region_in_bio(bio, io, region);
 
                 /*
                  * Try and add as many pages as possible.
@@ -337,6 +349,8 @@ static void dispatch_io(int rw, unsigned int num_regions,
         int i;
         struct dpages old_pages = *dp;
 
+        BUG_ON(num_regions > DM_IO_MAX_REGIONS);
+
         if (sync)
                 rw |= (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG);
 
@@ -361,7 +375,14 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
                    struct dm_io_region *where, int rw, struct dpages *dp,
                    unsigned long *error_bits)
 {
-        struct io io;
+        /*
+         * gcc <= 4.3 can't do the alignment for stack variables, so we must
+         * align it on our own.
+         * volatile prevents the optimizer from removing or reusing
+         * "io_" field from the stack frame (allowed in ANSI C).
+         */
+        volatile char io_[sizeof(struct io) + __alignof__(struct io) - 1];
+        struct io *io = (struct io *)PTR_ALIGN(&io_, __alignof__(struct io));
 
         if (num_regions > 1 && (rw & RW_MASK) != WRITE) {
                 WARN_ON(1);
@@ -369,33 +390,33 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
         }
 
 retry:
-        io.error_bits = 0;
-        io.eopnotsupp_bits = 0;
-        atomic_set(&io.count, 1); /* see dispatch_io() */
-        io.sleeper = current;
-        io.client = client;
+        io->error_bits = 0;
+        io->eopnotsupp_bits = 0;
+        atomic_set(&io->count, 1); /* see dispatch_io() */
+        io->sleeper = current;
+        io->client = client;
 
-        dispatch_io(rw, num_regions, where, dp, &io, 1);
+        dispatch_io(rw, num_regions, where, dp, io, 1);
 
         while (1) {
                 set_current_state(TASK_UNINTERRUPTIBLE);
 
-                if (!atomic_read(&io.count))
+                if (!atomic_read(&io->count))
                         break;
 
                 io_schedule();
         }
         set_current_state(TASK_RUNNING);
 
-        if (io.eopnotsupp_bits && (rw & (1 << BIO_RW_BARRIER))) {
+        if (io->eopnotsupp_bits && (rw & (1 << BIO_RW_BARRIER))) {
                 rw &= ~(1 << BIO_RW_BARRIER);
                 goto retry;
         }
 
         if (error_bits)
-                *error_bits = io.error_bits;
+                *error_bits = io->error_bits;
 
-        return io.error_bits ? -EIO : 0;
+        return io->error_bits ? -EIO : 0;
 }
 
 static int async_io(struct dm_io_client *client, unsigned int num_regions,