Re: [PATCH v2 20/21] btrfs: skip LOOP_NO_EMPTY_SIZE if not clustered allocation

From: Naohiro Aota <naohiro.aota@wdc.com>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org, David Sterba <dsterba@suse.com>,
	Chris Mason <clm@fb.com>, Nikolay Borisov <nborisov@suse.com>,
	Damien Le Moal <damien.lemoal@wdc.com>,
	Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
	Hannes Reinecke <hare@suse.com>,
	Anand Jain <anand.jain@oracle.com>,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 20/21] btrfs: skip LOOP_NO_EMPTY_SIZE if not clustered allocation
Date: Thu, 20 Feb 2020 18:56:31 +0900	[thread overview]
Message-ID: <20200220095631.7rlk7lmnp7np4nvg@naota.dhcp.fujisawa.hgst.com> (raw)
In-Reply-To: <b8908ae0-9e4d-5086-0d4c-768d45215695@toxicpanda.com>

On Thu, Feb 13, 2020 at 02:55:30PM -0500, Josef Bacik wrote:
>On 2/12/20 2:20 AM, Naohiro Aota wrote:
>>LOOP_NO_EMPTY_SIZE is solely dedicated for clustered allocation. So,
>>we can skip this stage and go to LOOP_GIVEUP stage to indicate we gave
>>up the allocation. This commit also moves the scope of the "clustered"
>>variable.
>>
>>Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>>---
>>  fs/btrfs/extent-tree.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>>diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>>index 8f0d489f76fa..3ab0d2f5d718 100644
>>--- a/fs/btrfs/extent-tree.c
>>+++ b/fs/btrfs/extent-tree.c
>>@@ -3373,6 +3373,7 @@ enum btrfs_loop_type {
>>  	LOOP_CACHING_WAIT,
>>  	LOOP_ALLOC_CHUNK,
>>  	LOOP_NO_EMPTY_SIZE,
>>+	LOOP_GIVEUP,
>
>Why do we need a new loop definition here?  Can we just return ENOSPC 
>and be done?  You don't appear to use it anywhere, so it doesn't seem 
>like it's needed.  Thanks,
>
>Josef

This is for other allocation policy to skip unnecessary loop stages
(e.g. LOOP_NO_EMPTY_SIZE) from an earlier stage. For example, zoned
allocation policy can implement the code below in
chunk_allocation_failed() to skip the following stages.

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4badfae0c932..0a18c09b078b 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3775,6 +3854,10 @@ static int chunk_allocation_failed(struct find_free_extent_ctl *ffe_ctl)
                  */
                 ffe_ctl->loop = LOOP_NO_EMPTY_SIZE;
                 return 0;
+       case BTRFS_EXTENT_ALLOC_ZONED:
+               /* give up here */
+               ffe_ctl->loop = LOOP_GIVEUP;
+               return -ENOSPC;
         default:
                 BUG();
         }

But, I can keep this LOOP_GIVEUP introduction patch later with this
zoned allocator ones.

Thanks,
