[PATCH] Btrfs: fix early ENOSPC due to delalloc

[PATCH] Btrfs: fix early ENOSPC due to delalloc

[Omar Sandoval]

From: Omar Sandoval <osandov@fb.com>

If a lot of metadata is reserved for outstanding delayed allocations, we
rely on shrink_delalloc() to reclaim metadata space in order to fulfill
reservation tickets. However, shrink_delalloc() has a shortcut where if
it determines that space can be overcommitted, it will stop early. This
made sense before the ticketed enospc system, but now it means that
shrink_delalloc() will often not reclaim enough space to fulfill any
tickets, leading to an early ENOSPC. (Reservation tickets don't care
about being able to overcommit, they need every byte accounted for.)

Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
all of the metadata it is supposed to. This fixes early ENOSPCs we were
seeing when doing a btrfs receive to populate a new filesystem.

Signed-off-by: Omar Sandoval <osandov@fb.com>
---
I don't have a good reproducer for this except for the btrfs send stream
I was given by someone internally, unfortunately.

 fs/btrfs/extent-tree.c | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 33d979e9ea2a..83eecd33ad96 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4776,10 +4776,6 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
 		else
 			flush = BTRFS_RESERVE_NO_FLUSH;
 		spin_lock(&space_info->lock);
-		if (can_overcommit(root, space_info, orig, flush)) {
-			spin_unlock(&space_info->lock);
-			break;
-		}
 		if (list_empty(&space_info->tickets) &&
 		    list_empty(&space_info->priority_tickets)) {
 			spin_unlock(&space_info->lock);
-- 
2.13.2

Re: [PATCH] Btrfs: fix early ENOSPC due to delalloc

[Omar Sandoval]

On Thu, Jul 06, 2017 at 10:59:27PM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> If a lot of metadata is reserved for outstanding delayed allocations, we
> rely on shrink_delalloc() to reclaim metadata space in order to fulfill
> reservation tickets. However, shrink_delalloc() has a shortcut where if
> it determines that space can be overcommitted, it will stop early. This
> made sense before the ticketed enospc system, but now it means that
> shrink_delalloc() will often not reclaim enough space to fulfill any
> tickets, leading to an early ENOSPC. (Reservation tickets don't care
> about being able to overcommit, they need every byte accounted for.)
> 
> Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
> all of the metadata it is supposed to. This fixes early ENOSPCs we were
> seeing when doing a btrfs receive to populate a new filesystem.

Jeff, Nikolay, did either of you get a chance to test this yet?

> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
> I don't have a good reproducer for this except for the btrfs send stream
> I was given by someone internally, unfortunately.
> 
>  fs/btrfs/extent-tree.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 33d979e9ea2a..83eecd33ad96 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -4776,10 +4776,6 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
>  		else
>  			flush = BTRFS_RESERVE_NO_FLUSH;
>  		spin_lock(&space_info->lock);
> -		if (can_overcommit(root, space_info, orig, flush)) {
> -			spin_unlock(&space_info->lock);
> -			break;
> -		}
>  		if (list_empty(&space_info->tickets) &&
>  		    list_empty(&space_info->priority_tickets)) {
>  			spin_unlock(&space_info->lock);
> -- 
> 2.13.2
> 

Re: [PATCH] Btrfs: fix early ENOSPC due to delalloc

[Nikolay Borisov]

On 15.07.2017 00:36, Omar Sandoval wrote:
> On Thu, Jul 06, 2017 at 10:59:27PM -0700, Omar Sandoval wrote:
>> From: Omar Sandoval <osandov@fb.com>
>>
>> If a lot of metadata is reserved for outstanding delayed allocations, we
>> rely on shrink_delalloc() to reclaim metadata space in order to fulfill
>> reservation tickets. However, shrink_delalloc() has a shortcut where if
>> it determines that space can be overcommitted, it will stop early. This
>> made sense before the ticketed enospc system, but now it means that
>> shrink_delalloc() will often not reclaim enough space to fulfill any
>> tickets, leading to an early ENOSPC. (Reservation tickets don't care
>> about being able to overcommit, they need every byte accounted for.)
>>
>> Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
>> all of the metadata it is supposed to. This fixes early ENOSPCs we were
>> seeing when doing a btrfs receive to populate a new filesystem.
> 
> Jeff, Nikolay, did either of you get a chance to test this yet?

I tested this patch with generic/273 and it didn't prevent ENOSPC there.

> 
>> Signed-off-by: Omar Sandoval <osandov@fb.com>
>> ---
>> I don't have a good reproducer for this except for the btrfs send stream
>> I was given by someone internally, unfortunately.
>>
>>  fs/btrfs/extent-tree.c | 4 ----
>>  1 file changed, 4 deletions(-)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index 33d979e9ea2a..83eecd33ad96 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -4776,10 +4776,6 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
>>  		else
>>  			flush = BTRFS_RESERVE_NO_FLUSH;
>>  		spin_lock(&space_info->lock);
>> -		if (can_overcommit(root, space_info, orig, flush)) {
>> -			spin_unlock(&space_info->lock);
>> -			break;
>> -		}
>>  		if (list_empty(&space_info->tickets) &&
>>  		    list_empty(&space_info->priority_tickets)) {
>>  			spin_unlock(&space_info->lock);
>> -- 
>> 2.13.2
>>
> 

Re: [PATCH] Btrfs: fix early ENOSPC due to delalloc

[Omar Sandoval]

On Sat, Jul 15, 2017 at 09:43:18AM +0300, Nikolay Borisov wrote:
> 
> 
> On 15.07.2017 00:36, Omar Sandoval wrote:
> > On Thu, Jul 06, 2017 at 10:59:27PM -0700, Omar Sandoval wrote:
> >> From: Omar Sandoval <osandov@fb.com>
> >>
> >> If a lot of metadata is reserved for outstanding delayed allocations, we
> >> rely on shrink_delalloc() to reclaim metadata space in order to fulfill
> >> reservation tickets. However, shrink_delalloc() has a shortcut where if
> >> it determines that space can be overcommitted, it will stop early. This
> >> made sense before the ticketed enospc system, but now it means that
> >> shrink_delalloc() will often not reclaim enough space to fulfill any
> >> tickets, leading to an early ENOSPC. (Reservation tickets don't care
> >> about being able to overcommit, they need every byte accounted for.)
> >>
> >> Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
> >> all of the metadata it is supposed to. This fixes early ENOSPCs we were
> >> seeing when doing a btrfs receive to populate a new filesystem.
> > 
> > Jeff, Nikolay, did either of you get a chance to test this yet?
> 
> I tested this patch with generic/273 and it didn't prevent ENOSPC there.

Weird, I've never seen generic/273 fail. Anyways, I'm more interested in
the installer ENOSPCs Jeff mentioned.

Re: [PATCH] Btrfs: fix early ENOSPC due to delalloc

[Nikolay Borisov]

On 15.07.2017 10:09, Omar Sandoval wrote:
> On Sat, Jul 15, 2017 at 09:43:18AM +0300, Nikolay Borisov wrote:
>>
>>
>> On 15.07.2017 00:36, Omar Sandoval wrote:
>>> On Thu, Jul 06, 2017 at 10:59:27PM -0700, Omar Sandoval wrote:
>>>> From: Omar Sandoval <osandov@fb.com>
>>>>
>>>> If a lot of metadata is reserved for outstanding delayed allocations, we
>>>> rely on shrink_delalloc() to reclaim metadata space in order to fulfill
>>>> reservation tickets. However, shrink_delalloc() has a shortcut where if
>>>> it determines that space can be overcommitted, it will stop early. This
>>>> made sense before the ticketed enospc system, but now it means that
>>>> shrink_delalloc() will often not reclaim enough space to fulfill any
>>>> tickets, leading to an early ENOSPC. (Reservation tickets don't care
>>>> about being able to overcommit, they need every byte accounted for.)
>>>>
>>>> Fix it by getting rid of the shortcut so that shrink_delalloc() reclaims
>>>> all of the metadata it is supposed to. This fixes early ENOSPCs we were
>>>> seeing when doing a btrfs receive to populate a new filesystem.
>>>
>>> Jeff, Nikolay, did either of you get a chance to test this yet?
>>
>> I tested this patch with generic/273 and it didn't prevent ENOSPC there.
> 
> Weird, I've never seen generic/273 fail. Anyways, I'm more interested in
> the installer ENOSPCs Jeff mentioned.

It's failing even on current upstream kernels with premature ENOSPC.

>