[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <9ab48353-2033-4ab6-8334-28859d5e9e0f@wdc.com>
Date: Tue, 23 Jan 2024 07:49:22 +0000
From: Johannes Thumshirn <Johannes.Thumshirn@....com>
To: "dsterba@...e.cz" <dsterba@...e.cz>
CC: Josef Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>,
Naohiro Aota <Naohiro.Aota@....com>, "linux-btrfs@...r.kernel.org"
<linux-btrfs@...r.kernel.org>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>, Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [PATCH 1/2] btrfs: zoned: use rcu list for iterating devices to
collect stats
On 22.01.24 22:35, David Sterba wrote:
> On Mon, Jan 22, 2024 at 02:51:03AM -0800, Johannes Thumshirn wrote:
>> As btrfs_zoned_should_reclaim only has to iterate the device list in order
>> to collect stats on the device's total and used bytes, we don't need to
>> take the full blown mutex, but can iterate the device list in a rcu_read
>> context.
>>
>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
>> ---
>> fs/btrfs/zoned.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
>> index 168af9d000d1..b7e7b5a5a6fa 100644
>> --- a/fs/btrfs/zoned.c
>> +++ b/fs/btrfs/zoned.c
>> @@ -2423,15 +2423,15 @@ bool btrfs_zoned_should_reclaim(struct btrfs_fs_info *fs_info)
>> if (fs_info->bg_reclaim_threshold == 0)
>> return false;
>>
>> - mutex_lock(&fs_devices->device_list_mutex);
>> - list_for_each_entry(device, &fs_devices->devices, dev_list) {
>> + rcu_read_lock();
>> + list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {
>> if (!device->bdev)
>> continue;
>>
>> total += device->disk_total_bytes;
>> used += device->bytes_used;
>> }
>> - mutex_unlock(&fs_devices->device_list_mutex);
>> + rcu_read_unlock();
>
> This is basically only a hint and inaccuracies in the total or used
> values would be transient, right? The sum is calculated each time the
> funciton is called, not stored anywhere so in the unlikely case of
> device removal it may skip reclaim once, but then pick it up later.
> Any actual removal of the block groups in verified again and properly
> locked in btrfs_reclaim_bgs_work().
>
Yes.
Powered by blists - more mailing lists