[PATCH]Btrfs:Fix discard semantic

[PATCH]Btrfs:Fix discard semantic

[Liu Hui]

Hi,
This is a patch to fix discard semantic to make Btrfs work with FTL(or
SSD?). As we know, we can improve FTL's performance by telling it
which sectors are freed by file system. But if we don't tell FTL the
information of free sectors in proper time, the transaction mechanism
of Btrfs will be destroyed and Btrfs could not roll back the previous
transaction under the power loss condition.

There are some problems in the old implementation:
1, In __free_extent(), the pinned down extents should not be discarded.
2, In free_extents(), the free extents are all pinned, so they need to
be discarded in transaction committing time instead of free_extents().
3, The reserved extent used by log tree should be discard too.

This patch change discard behavior as follows:
1, In __free_extent, we only discard the unpinned extent.
2, Delay discarding the pinned extent in btrfs_finish_extent_commit()
when committing transaction.
3, Remove discarding from free_extents()
4, Add discard interface into btrfs_free_reserved_extent()
5, Discard sectors before updating the free space cache, otherwise,
FTL will destroy file system data.

-- 
Thanks & Best Regards
Liu Hui
--

diff --git a/extent-tree.c b/extent-tree.c
index fe0e59a..7247b16 100644
--- a/extent-tree.c
+++ b/extent-tree.c
@@ -874,6 +874,34 @@ static void btrfs_issue_discard(struct block_device *bdev,
 	blkdev_issue_discard(bdev, start >> 9, len >> 9);
 #endif
 }
+
+static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
+				u64 num_bytes)
+{
+	int ret;
+	u64 map_length = num_bytes;
+	struct btrfs_multi_bio *multi = NULL;
+
+	/* Tell the block device(s) that the sectors can be discarded */
+	ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
+			      bytenr, &map_length, &multi, 0);
+	if (!ret) {
+		struct btrfs_bio_stripe *stripe = multi->stripes;
+		int i;
+
+		if (map_length > num_bytes)
+			map_length = num_bytes;
+
+		for (i = 0; i < multi->num_stripes; i++, stripe++) {
+			btrfs_issue_discard(stripe->dev->bdev,
+					    stripe->physical,
+					    map_length);
+		}
+		kfree(multi);
+	}
+
+	return ret;
+}
 #endif

 static int noinline free_extents(struct btrfs_trans_handle *trans,
@@ -1069,10 +1097,6 @@ search:
 		for (pos = cur, n = pos->next; pos != end;
 		     pos = n, n = pos->next) {
 			struct pending_extent_op *tmp;
-#ifdef BIO_RW_DISCARD
-			u64 map_length;
-			struct btrfs_multi_bio *multi = NULL;
-#endif
 			tmp = list_entry(pos, struct pending_extent_op, list);

 			/*
@@ -1084,28 +1108,6 @@ search:
 						 tmp->del);
 			BUG_ON(ret);

-#ifdef BIO_RW_DISCARD
-			map_length = tmp->num_bytes;
-			ret = btrfs_map_block(&info->mapping_tree, READ,
-					      tmp->bytenr, &map_length, &multi,
-					      0);
-			if (!ret) {
-				struct btrfs_bio_stripe *stripe;
-				int i;
-
-				stripe = multi->stripes;
-
-				if (map_length > tmp->num_bytes)
-					map_length = tmp->num_bytes;
-
-				for (i = 0; i < multi->num_stripes;
-				     i++, stripe++)
-					btrfs_issue_discard(stripe->dev->bdev,
-							    stripe->physical,
-							    map_length);
-				kfree(multi);
-			}
-#endif
 			list_del_init(&tmp->list);
 			unlock_extent(&info->extent_ins, tmp->bytenr,
 				      tmp->bytenr + tmp->num_bytes - 1,
@@ -2104,8 +2106,14 @@ int btrfs_finish_extent_commit(struct
btrfs_trans_handle *trans,
 					    EXTENT_DIRTY);
 		if (ret)
 			break;
+
+#ifdef BIO_RW_DISCARD
+		ret = btrfs_discard_extent(root, start, end + 1 - start);
+#endif
+
 		btrfs_update_pinned_extents(root, start, end + 1 - start, 0);
 		clear_extent_dirty(unpin, start, end, GFP_NOFS);
+
 		if (need_resched()) {
 			mutex_unlock(&root->fs_info->pinned_mutex);
 			cond_resched();
@@ -2113,7 +2121,7 @@ int btrfs_finish_extent_commit(struct
btrfs_trans_handle *trans,
 		}
 	}
 	mutex_unlock(&root->fs_info->pinned_mutex);
-	return 0;
+	return ret;
 }

 static int finish_current_insert(struct btrfs_trans_handle *trans,
@@ -2458,10 +2466,6 @@ static int __free_extent(struct
btrfs_trans_handle *trans,
 	if (refs == 0) {
 		u64 super_used;
 		u64 root_used;
-#ifdef BIO_RW_DISCARD
-		u64 map_length = num_bytes;
-		struct btrfs_multi_bio *multi = NULL;
-#endif

 		if (pin) {
 			mutex_lock(&root->fs_info->pinned_mutex);
@@ -2493,28 +2497,15 @@ static int __free_extent(struct
btrfs_trans_handle *trans,
 			BUG_ON(ret);
 		}

-		ret = update_block_group(trans, root, bytenr, num_bytes, 0,
-					 mark_free);
-		BUG_ON(ret);
 #ifdef BIO_RW_DISCARD
-		/* Tell the block device(s) that the sectors can be discarded */
-		ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
-				      bytenr, &map_length, &multi, 0);
-		if (!ret) {
-			struct btrfs_bio_stripe *stripe = multi->stripes;
-			int i;
-
-			if (map_length > num_bytes)
-				map_length = num_bytes;
-
-			for (i = 0; i < multi->num_stripes; i++, stripe++) {
-				btrfs_issue_discard(stripe->dev->bdev,
-						    stripe->physical,
-						     map_length);
-			}
-			kfree(multi);
+		if (!pin) {
+			ret = btrfs_discard_extent(root, bytenr, num_bytes);
 		}
 #endif
+
+		ret = update_block_group(trans, root, bytenr, num_bytes, 0,
+					 mark_free);
+		BUG_ON(ret);
 	}
 	btrfs_free_path(path);
 	finish_current_insert(trans, extent_root, 0);
@@ -3112,16 +3103,23 @@ again:
 int btrfs_free_reserved_extent(struct btrfs_root *root, u64 start, u64 len)
 {
 	struct btrfs_block_group_cache *cache;
+	int ret = 0;

 	cache = btrfs_lookup_block_group(root->fs_info, start);
 	if (!cache) {
 		printk(KERN_ERR "Unable to find block group for %Lu\n", start);
 		return -ENOSPC;
 	}
+
+#ifdef BIO_RW_DISCARD
+	ret = btrfs_discard_extent(root, start, len);
+#endif
+
 	btrfs_add_free_space(cache, start, len);
 	put_block_group(cache);
 	update_reserved_extents(root, start, len, 0);
-	return 0;
+
+	return ret;
 }

 int btrfs_reserve_extent(struct btrfs_trans_handle *trans,

Re: [PATCH]Btrfs:Fix discard semantic

[Yan Zheng]

2008/12/29 Liu Hui <onlyflyer@gmail.com>:
> Hi,
> This is a patch to fix discard semantic to make Btrfs work with FTL(or
> SSD?). As we know, we can improve FTL's performance by telling it
> which sectors are freed by file system. But if we don't tell FTL the
> information of free sectors in proper time, the transaction mechanism
> of Btrfs will be destroyed and Btrfs could not roll back the previous
> transaction under the power loss condition.
>
> There are some problems in the old implementation:
> 1, In __free_extent(), the pinned down extents should not be discarded.
> 2, In free_extents(), the free extents are all pinned, so they need to
> be discarded in transaction committing time instead of free_extents().
> 3, The reserved extent used by log tree should be discard too.
>
> This patch change discard behavior as follows:
> 1, In __free_extent, we only discard the unpinned extent.
> 2, Delay discarding the pinned extent in btrfs_finish_extent_commit()
> when committing transaction.
> 3, Remove discarding from free_extents()
> 4, Add discard interface into btrfs_free_reserved_extent()
> 5, Discard sectors before updating the free space cache, otherwise,
> FTL will destroy file system data.
>
> --
> Thanks & Best Regards
> Liu Hui
> --

Hi Liu Hui, your patch is malformed, please re-send it.

>
> diff --git a/extent-tree.c b/extent-tree.c
> index fe0e59a..7247b16 100644
> --- a/extent-tree.c
> +++ b/extent-tree.c
> @@ -874,6 +874,34 @@ static void btrfs_issue_discard(struct block_device *bdev,
>        blkdev_issue_discard(bdev, start >> 9, len >> 9);
>  #endif
>  }
> +
> +static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
> +                               u64 num_bytes)
> +{
> +       int ret;
> +       u64 map_length = num_bytes;
> +       struct btrfs_multi_bio *multi = NULL;
> +
> +       /* Tell the block device(s) that the sectors can be discarded */
> +       ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
> +                             bytenr, &map_length, &multi, 0);
> +       if (!ret) {
> +               struct btrfs_bio_stripe *stripe = multi->stripes;
> +               int i;
> +
> +               if (map_length > num_bytes)
> +                       map_length = num_bytes;
> +
> +               for (i = 0; i < multi->num_stripes; i++, stripe++) {
> +                       btrfs_issue_discard(stripe->dev->bdev,
> +                                           stripe->physical,
> +                                           map_length);
> +               }
> +               kfree(multi);
> +       }
> +
> +       return ret;
> +}
>  #endif
>
>  static int noinline free_extents(struct btrfs_trans_handle *trans,
> @@ -1069,10 +1097,6 @@ search:
>                for (pos = cur, n = pos->next; pos != end;
>                     pos = n, n = pos->next) {
>                        struct pending_extent_op *tmp;
> -#ifdef BIO_RW_DISCARD
> -                       u64 map_length;
> -                       struct btrfs_multi_bio *multi = NULL;
> -#endif
>                        tmp = list_entry(pos, struct pending_extent_op, list);
>
>                        /*
> @@ -1084,28 +1108,6 @@ search:
>                                                 tmp->del);
>                        BUG_ON(ret);
>
> -#ifdef BIO_RW_DISCARD
> -                       map_length = tmp->num_bytes;
> -                       ret = btrfs_map_block(&info->mapping_tree, READ,
> -                                             tmp->bytenr, &map_length, &multi,
> -                                             0);
> -                       if (!ret) {
> -                               struct btrfs_bio_stripe *stripe;
> -                               int i;
> -
> -                               stripe = multi->stripes;
> -
> -                               if (map_length > tmp->num_bytes)
> -                                       map_length = tmp->num_bytes;
> -
> -                               for (i = 0; i < multi->num_stripes;
> -                                    i++, stripe++)
> -                                       btrfs_issue_discard(stripe->dev->bdev,
> -                                                           stripe->physical,
> -                                                           map_length);
> -                               kfree(multi);
> -                       }
> -#endif
>                        list_del_init(&tmp->list);
>                        unlock_extent(&info->extent_ins, tmp->bytenr,
>                                      tmp->bytenr + tmp->num_bytes - 1,
> @@ -2104,8 +2106,14 @@ int btrfs_finish_extent_commit(struct
> btrfs_trans_handle *trans,
>                                            EXTENT_DIRTY);
>                if (ret)
>                        break;
> +
> +#ifdef BIO_RW_DISCARD
> +               ret = btrfs_discard_extent(root, start, end + 1 - start);
> +#endif
> +
>                btrfs_update_pinned_extents(root, start, end + 1 - start, 0);
>                clear_extent_dirty(unpin, start, end, GFP_NOFS);
> +
>                if (need_resched()) {
>                        mutex_unlock(&root->fs_info->pinned_mutex);
>                        cond_resched();
> @@ -2113,7 +2121,7 @@ int btrfs_finish_extent_commit(struct
> btrfs_trans_handle *trans,
>                }
>        }
>        mutex_unlock(&root->fs_info->pinned_mutex);
> -       return 0;
> +       return ret;
>  }
>
>  static int finish_current_insert(struct btrfs_trans_handle *trans,
> @@ -2458,10 +2466,6 @@ static int __free_extent(struct
> btrfs_trans_handle *trans,
>        if (refs == 0) {
>                u64 super_used;
>                u64 root_used;
> -#ifdef BIO_RW_DISCARD
> -               u64 map_length = num_bytes;
> -               struct btrfs_multi_bio *multi = NULL;
> -#endif
>
>                if (pin) {
>                        mutex_lock(&root->fs_info->pinned_mutex);
> @@ -2493,28 +2497,15 @@ static int __free_extent(struct
> btrfs_trans_handle *trans,
>                        BUG_ON(ret);
>                }
>
> -               ret = update_block_group(trans, root, bytenr, num_bytes, 0,
> -                                        mark_free);
> -               BUG_ON(ret);
>  #ifdef BIO_RW_DISCARD
> -               /* Tell the block device(s) that the sectors can be discarded */
> -               ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
> -                                     bytenr, &map_length, &multi, 0);
> -               if (!ret) {
> -                       struct btrfs_bio_stripe *stripe = multi->stripes;
> -                       int i;
> -
> -                       if (map_length > num_bytes)
> -                               map_length = num_bytes;
> -
> -                       for (i = 0; i < multi->num_stripes; i++, stripe++) {
> -                               btrfs_issue_discard(stripe->dev->bdev,
> -                                                   stripe->physical,
> -                                                    map_length);
> -                       }
> -                       kfree(multi);
> +               if (!pin) {
> +                       ret = btrfs_discard_extent(root, bytenr, num_bytes);
>                }

We should check 'mark_free' instead of 'pin' here

>  #endif
> +
> +               ret = update_block_group(trans, root, bytenr, num_bytes, 0,
> +                                        mark_free);
> +               BUG_ON(ret);
>        }
>        btrfs_free_path(path);
>        finish_current_insert(trans, extent_root, 0);
> @@ -3112,16 +3103,23 @@ again:
>  int btrfs_free_reserved_extent(struct btrfs_root *root, u64 start, u64 len)
>  {
>        struct btrfs_block_group_cache *cache;
> +       int ret = 0;
>
>        cache = btrfs_lookup_block_group(root->fs_info, start);
>        if (!cache) {
>                printk(KERN_ERR "Unable to find block group for %Lu\n", start);
>                return -ENOSPC;
>        }
> +
> +#ifdef BIO_RW_DISCARD
> +       ret = btrfs_discard_extent(root, start, len);
> +#endif
> +
>        btrfs_add_free_space(cache, start, len);
>        put_block_group(cache);
>        update_reserved_extents(root, start, len, 0);
> -       return 0;
> +
> +       return ret;
>  }
>
>  int btrfs_reserve_extent(struct btrfs_trans_handle *trans,

Re: [PATCH]Btrfs:Fix discard semantic

[Liu Hui]

Hi Yan Zheng,

Thanks in advance!

Here are the new description and the new patch(based on standalone git tree):


This is a patch to fix discard semantic to make Btrfs work with FTL(or
SSD?). As we know, we can improve FTL's performance by telling it
which sectors are freed by file system. But if we don't tell FTL the
information of free sectors in proper time, the transaction mechanism
of Btrfs will be destroyed and Btrfs could not roll back the previous
transaction under the power loss condition.

There are some problems in the old implementation:
1, In __free_extent(), the pinned down extents should not be discarded.
2, In free_extents(), the free extents are all pinned, so they need to
be discarded in transaction committing time instead of free_extents().
3, The reserved extent used by log tree should be discard too.

This patch change discard behavior as follows:
1, For the extents which need to be free at once,
   we discard them in update_block_group().
2, Delay discarding the pinned extent in btrfs_finish_extent_commit()
   when committing transaction.
3, Remove discarding from free_extents() and __free_extent()
4, Add discard interface into btrfs_free_reserved_extent()
5, Discard sectors before updating the free space cache, otherwise,
   FTL will destroy file system data.

--
Thanks & Best Regards
Liu Hui
--

--- extent-tree-old.c	2009-01-03 23:01:30.000000000 +0800
+++ extent-tree.c	2009-01-03 22:58:55.000000000 +0800
@@ -874,6 +874,34 @@
 	blkdev_issue_discard(bdev, start >> 9, len >> 9);
 #endif
 }
+
+static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
+				u64 num_bytes)
+{
+	int ret;
+	u64 map_length = num_bytes;
+	struct btrfs_multi_bio *multi = NULL;
+
+	/* Tell the block device(s) that the sectors can be discarded */
+	ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
+			      bytenr, &map_length, &multi, 0);
+	if (!ret) {
+		struct btrfs_bio_stripe *stripe = multi->stripes;
+		int i;
+
+		if (map_length > num_bytes)
+			map_length = num_bytes;
+
+		for (i = 0; i < multi->num_stripes; i++, stripe++) {
+			btrfs_issue_discard(stripe->dev->bdev,
+					    stripe->physical,
+					    map_length);
+		}
+		kfree(multi);
+	}
+
+	return ret;
+}
 #endif

 static int noinline free_extents(struct btrfs_trans_handle *trans,
@@ -1069,10 +1097,6 @@
 		for (pos = cur, n = pos->next; pos != end;
 		     pos = n, n = pos->next) {
 			struct pending_extent_op *tmp;
-#ifdef BIO_RW_DISCARD
-			u64 map_length;
-			struct btrfs_multi_bio *multi = NULL;
-#endif
 			tmp = list_entry(pos, struct pending_extent_op, list);

 			/*
@@ -1084,28 +1108,6 @@
 						 tmp->del);
 			BUG_ON(ret);

-#ifdef BIO_RW_DISCARD
-			map_length = tmp->num_bytes;
-			ret = btrfs_map_block(&info->mapping_tree, READ,
-					      tmp->bytenr, &map_length, &multi,
-					      0);
-			if (!ret) {
-				struct btrfs_bio_stripe *stripe;
-				int i;
-
-				stripe = multi->stripes;
-
-				if (map_length > tmp->num_bytes)
-					map_length = tmp->num_bytes;
-
-				for (i = 0; i < multi->num_stripes;
-				     i++, stripe++)
-					btrfs_issue_discard(stripe->dev->bdev,
-							    stripe->physical,
-							    map_length);
-				kfree(multi);
-			}
-#endif
 			list_del_init(&tmp->list);
 			unlock_extent(&info->extent_ins, tmp->bytenr,
 				      tmp->bytenr + tmp->num_bytes - 1,
@@ -1965,6 +1967,13 @@
 			spin_unlock(&cache->space_info->lock);
 			if (mark_free) {
 				int ret;
+
+#ifdef BIO_RW_DISCARD
+				ret = btrfs_discard_extent(root, bytenr,
+							   num_bytes);
+				WARN_ON(ret);
+#endif
+
 				ret = btrfs_add_free_space(cache, bytenr,
 							   num_bytes);
 				WARN_ON(ret);
@@ -2104,8 +2113,14 @@
 					    EXTENT_DIRTY);
 		if (ret)
 			break;
+
+#ifdef BIO_RW_DISCARD
+		ret = btrfs_discard_extent(root, start, end + 1 - start);
+#endif
+
 		btrfs_update_pinned_extents(root, start, end + 1 - start, 0);
 		clear_extent_dirty(unpin, start, end, GFP_NOFS);
+
 		if (need_resched()) {
 			mutex_unlock(&root->fs_info->pinned_mutex);
 			cond_resched();
@@ -2113,7 +2128,7 @@
 		}
 	}
 	mutex_unlock(&root->fs_info->pinned_mutex);
-	return 0;
+	return ret;
 }

 static int finish_current_insert(struct btrfs_trans_handle *trans,
@@ -2458,10 +2473,6 @@
 	if (refs == 0) {
 		u64 super_used;
 		u64 root_used;
-#ifdef BIO_RW_DISCARD
-		u64 map_length = num_bytes;
-		struct btrfs_multi_bio *multi = NULL;
-#endif

 		if (pin) {
 			mutex_lock(&root->fs_info->pinned_mutex);
@@ -2496,25 +2507,6 @@
 		ret = update_block_group(trans, root, bytenr, num_bytes, 0,
 					 mark_free);
 		BUG_ON(ret);
-#ifdef BIO_RW_DISCARD
-		/* Tell the block device(s) that the sectors can be discarded */
-		ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
-				      bytenr, &map_length, &multi, 0);
-		if (!ret) {
-			struct btrfs_bio_stripe *stripe = multi->stripes;
-			int i;
-
-			if (map_length > num_bytes)
-				map_length = num_bytes;
-
-			for (i = 0; i < multi->num_stripes; i++, stripe++) {
-				btrfs_issue_discard(stripe->dev->bdev,
-						    stripe->physical,
-						     map_length);
-			}
-			kfree(multi);
-		}
-#endif
 	}
 	btrfs_free_path(path);
 	finish_current_insert(trans, extent_root, 0);
@@ -3112,16 +3104,23 @@
 int btrfs_free_reserved_extent(struct btrfs_root *root, u64 start, u64 len)
 {
 	struct btrfs_block_group_cache *cache;
+	int ret = 0;

 	cache = btrfs_lookup_block_group(root->fs_info, start);
 	if (!cache) {
 		printk(KERN_ERR "Unable to find block group for %Lu\n", start);
 		return -ENOSPC;
 	}
+
+#ifdef BIO_RW_DISCARD
+	ret = btrfs_discard_extent(root, start, len);
+#endif
+
 	btrfs_add_free_space(cache, start, len);
 	put_block_group(cache);
 	update_reserved_extents(root, start, len, 0);
-	return 0;
+
+	return ret;
 }

 int btrfs_reserve_extent(struct btrfs_trans_handle *trans,

Re: [PATCH]Btrfs:Fix discard semantic

[Chris Mason]

On Sat, 2009-01-03 at 23:33 +0800, Liu Hui wrote:
> Hi Yan Zheng,
> 
> Thanks in advance!
> 
> Here are the new description and the new patch(based on standalone git tree):
> 

Thanks for fixing this up, I'll give it a try here.

-chris

Re: [PATCH]Btrfs:Fix discard semantic

[David Woodhouse]

On Sat, 2009-01-03 at 23:33 +0800, Liu Hui wrote:
> +       /* Tell the block device(s) that the sectors can be discarded */
> +       ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
> +                             bytenr, &map_length, &multi, 0);

Shouldn't that READ be a WRITE, if we want to discard every stripe of a
RAID1 rather than only one of them?

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation

[PATCH] btrfs: Fix partial discard on RAID1

[David Woodhouse]

In btrfs_discard_extent() we were only discarding half of a RAID1 or
RAID10 extent.

We should be telling btrfs_map_block() that we want to write, so it
tells us about _all_ mirrors. If we tell it we're going to read, it'll
only tell us about a single mirror at a time.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
---
Untested. Does anyone have any real devices that do TRIM yet, or do I
need to hack up an FTL to do it again?

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a5aca39..1496925 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1421,7 +1421,7 @@ static int btrfs_discard_extent(struct btrfs_root
*root, u64 bytenr,
 	struct btrfs_multi_bio *multi = NULL;
 
 	/* Tell the block device(s) that the sectors can be discarded */
-	ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
+	ret = btrfs_map_block(&root->fs_info->mapping_tree, WRITE,
 			      bytenr, &map_length, &multi, 0);
 	if (!ret) {
 		struct btrfs_bio_stripe *stripe = multi->stripes;

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation

Re: [PATCH] btrfs: Fix partial discard on RAID1

[Jens Axboe]

On Fri, Jul 10 2009, David Woodhouse wrote:
> In btrfs_discard_extent() we were only discarding half of a RAID1 or
> RAID10 extent.
> 
> We should be telling btrfs_map_block() that we want to write, so it
> tells us about _all_ mirrors. If we tell it we're going to read, it'll
> only tell us about a single mirror at a time.
> 
> Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
> ---
> Untested. Does anyone have any real devices that do TRIM yet, or do I
> need to hack up an FTL to do it again?

Get one of the OCZ vertex drives, they do trim. They use their own
opcode for it, but it's there.

-- 
Jens Axboe

Re: [PATCH]Btrfs:Fix discard semantic

[David Woodhouse]

On Thu, 2009-07-09 at 23:57 +0100, David Woodhouse wrote:
> On Sat, 2009-01-03 at 23:33 +0800, Liu Hui wrote:
> > +       /* Tell the block device(s) that the sectors can be discarded */
> > +       ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
> > +                             bytenr, &map_length, &multi, 0);
> 
> Shouldn't that READ be a WRITE, if we want to discard every stripe of a
> RAID1 rather than only one of them?

Actually it's more broken than that -- it will only discard the first
stripe_len of the extent. For any kind of RAID, including RAID0, we need
to loop over the btrfs_map_block() call.

I'll fix that too...

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation