lustre/kernel_patches/patches/raid5-serialize-ovelapping-reqs.patch

   1 RAID5 wasn't designed to support overlapping requests because
   2 in Linux all I/Os are serialized by page/buffer lock.  As Lustre
   3 doesn't use pagecache on server, we need to serialize I/Os in RAID5.
   4
   5 Index: linux-2.6.9/include/linux/raid/raid5.h
   6 ===================================================================
   7 --- linux-2.6.9.orig/include/linux/raid/raid5.h 2006-05-22 00:11:21.000000000 +0400
   8 +++ linux-2.6.9/include/linux/raid/raid5.h      2006-05-22 00:11:21.000000000 +0400
   9 @@ -134,6 +134,7 @@ struct stripe_head {
  10         unsigned long           state;                  /* state flags */
  11         atomic_t                count;                  /* nr of active thread/requests */
  12         spinlock_t              lock;
  13 +       wait_queue_head_t       wait;                   /* waitchan for overlapped bio's */
  14         struct r5dev {
  15                 struct bio      req;
  16                 struct bio_vec  vec;
  17 Index: linux-2.6.9/drivers/md/raid5.c
  18 ===================================================================
  19 --- linux-2.6.9.orig/drivers/md/raid5.c 2006-05-22 00:11:21.000000000 +0400
  20 +++ linux-2.6.9/drivers/md/raid5.c      2006-05-22 00:19:27.000000000 +0400
  21 @@ -308,6 +308,7 @@ static int grow_stripes(raid5_conf_t *co
  22                 memset(sh, 0, sizeof(*sh) + (devs-1)*sizeof(struct r5dev));
  23                 sh->raid_conf = conf;
  24                 sh->lock = SPIN_LOCK_UNLOCKED;
  25 +               init_waitqueue_head(&sh->wait);
  26
  27                 if (grow_buffers(sh, conf->raid_disks)) {
  28                         shrink_buffers(sh, conf->raid_disks);
  29 @@ -878,6 +879,9 @@ static void compute_parity(struct stripe
  30                 set_bit(R5_LOCKED,   &sh->dev[pd_idx].flags);
  31         } else
  32                 clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
  33 +
  34 +       /* probably someone waits for our completion? */
  35 +       wake_up(&sh->wait);
  36  }
  37
  38  /*
  39 @@ -885,7 +889,7 @@ static void compute_parity(struct stripe
  40   * toread/towrite point to the first in a chain.
  41   * The bi_next chain must be in order.
  42   */
  43 -static void add_stripe_bio (struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
  44 +static int add_stripe_bio (struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
  45  {
  46         struct bio **bip;
  47         raid5_conf_t *conf = sh->raid_conf;
  48 @@ -894,13 +898,21 @@ static void add_stripe_bio (struct strip
  49                 (unsigned long long)bi->bi_sector,
  50                 (unsigned long long)sh->sector);
  51
  52 -
  53         spin_lock(&sh->lock);
  54         spin_lock_irq(&conf->device_lock);
  55         if (forwrite)
  56                 bip = &sh->dev[dd_idx].towrite;
  57         else
  58                 bip = &sh->dev[dd_idx].toread;
  59 +
  60 +#if 1
  61 +       if (*bip) {
  62 +               /* overlapping bio, let's wait till first one is completed */
  63 +               spin_unlock_irq(&conf->device_lock);
  64 +               spin_unlock(&sh->lock);
  65 +               return 1;
  66 +       }
  67 +#else
  68         while (*bip && (*bip)->bi_sector < bi->bi_sector) {
  69                 BUG_ON((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector);
  70                 bip = & (*bip)->bi_next;
  71 @@ -910,6 +922,7 @@ static void add_stripe_bio (struct strip
  72                 BUG();
  73         if (*bip)
  74                 bi->bi_next = *bip;
  75 +#endif
  76         *bip = bi;
  77         bi->bi_phys_segments ++;
  78         spin_unlock_irq(&conf->device_lock);
  79 @@ -932,6 +945,7 @@ static void add_stripe_bio (struct strip
  80                 if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
  81                         set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
  82         }
  83 +       return 0;
  84  }
  85
  86  /*
  87 @@ -1014,6 +1028,7 @@ static void handle_stripe(struct stripe_
  88                         rbi = dev->toread;
  89                         dev->toread = NULL;
  90                         spin_unlock_irq(&conf->device_lock);
  91 +                       wake_up(&sh->wait);
  92                         while (rbi && rbi->bi_sector < dev->sector + STRIPE_SECTORS) {
  93                                 copy_data(0, rbi, dev->page, dev->sector);
  94                                 rbi2 = r5_next_bio(rbi, dev->sector);
  95 @@ -1059,6 +1074,7 @@ static void handle_stripe(struct stripe_
  96                         bi = sh->dev[i].towrite;
  97                         sh->dev[i].towrite = NULL;
  98                         if (bi) to_write--;
  99 +                       wake_up(&sh->wait);
 100
 101                         while (bi && bi->bi_sector < sh->dev[i].sector + STRIPE_SECTORS){
 102                                 struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
 103 @@ -1511,6 +1527,16 @@ static inline void raid5_plug_device(rai
 104         spin_unlock_irq(&conf->device_lock);
 105  }
 106
 107 +static inline void raid5_wait_stripe(struct stripe_head *sh, int dd_idx, int forwrite)
 108 +{
 109 +       struct bio **bip;
 110 +       if (forwrite)
 111 +               bip = &sh->dev[dd_idx].towrite;
 112 +       else
 113 +               bip = &sh->dev[dd_idx].toread;
 114 +       wait_event(sh->wait, *bip == NULL);
 115 +}
 116 +
 117  static int make_request (request_queue_t *q, struct bio * bi)
 118  {
 119         mddev_t *mddev = q->queuedata;
 120 @@ -1580,6 +1606,7 @@ repeat:
 121                                  * if we can't, then it's time to submit
 122                                  * all collected bio's in order to free
 123                                  * some space in the cache -bzzz */
 124 +try_stripe:
 125                                 sh = get_active_stripe(conf, new_sector, pd_idx, 1);
 126                                 if (!sh && !(bi->bi_rw&RWA_MASK)) {
 127                                         raid5_flush_bios(conf, bios, raid_disks);
 128 @@ -1587,7 +1614,11 @@ repeat:
 129                                 }
 130                         }
 131                         if (sh) {
 132 -                               add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK));
 133 +                               if (add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
 134 +                                       release_stripe(sh);
 135 +                                       raid5_wait_stripe(sh, dd_idx, bi->bi_rw&RW_MASK);
 136 +                                       goto try_stripe;
 137 +                               }
 138                         } else {
 139                                 /* cannot get stripe for read-ahead, just give-up */
 140                                 clear_bit(BIO_UPTODATE, &bi->bi_flags);