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From: Josef Bacik <josef@toxicpanda.com>
To: Qu Wenruo <wqu@suse.com>, linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v6 3/5] btrfs: statfs: Use pre-calculated per-profile available space
Date: Thu, 16 Jan 2020 11:21:31 -0500
Message-ID: <fd33e06c-6e4b-9117-28e3-323c4e103aaf@toxicpanda.com> (raw)
In-Reply-To: <20200116060404.95200-4-wqu@suse.com>

On 1/16/20 1:04 AM, Qu Wenruo wrote:
> Although btrfs_calc_avail_data_space() is trying to do an estimation
> on how many data chunks it can allocate, the estimation is far from
> perfect:
> 
> - Metadata over-commit is not considered at all
> - Chunk allocation doesn't take RAID5/6 into consideration
> 
> This patch will change btrfs_calc_avail_data_space() to use
> pre-calculated per-profile available space.
> 
> This provides the following benefits:
> - Accurate unallocated data space estimation, including RAID5/6
>    It's as accurate as chunk allocator, and can handle RAID5/6.
> 
> Although it still can't handle metadata over-commit that accurately, we
> still have fallback method for over-commit, by using factor based
> estimation.
> 
> The good news is, over-commit can only happen when we have enough
> unallocated space, so even we may not report byte accurate result when
> the fs is empty, the result will get more and more accurate when
> unallocated space is reducing.
> 
> So the metadata over-commit shouldn't cause too many problem.
> 
> Since we're keeping the old lock-free design, statfs should not experience
> any extra delay.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16  6:03 [PATCH v6 0/4] Introduce per-profile available space array to avoid over-confident can_overcommit() Qu Wenruo
2020-01-16  6:04 ` [PATCH v6 1/5] btrfs: Introduce per-profile available space facility Qu Wenruo
2020-01-16 16:14   ` Josef Bacik
2020-01-17  0:55     ` Qu Wenruo
2020-01-17  1:50       ` Josef Bacik
2020-01-17  1:54         ` Qu Wenruo
2020-01-17  2:00           ` Josef Bacik
2020-01-16  6:04 ` [PATCH v6 2/5] btrfs: space-info: Use per-profile available space in can_overcommit() Qu Wenruo
2020-01-16  6:04 ` [PATCH v6 3/5] btrfs: statfs: Use pre-calculated per-profile available space Qu Wenruo
2020-01-16 16:21   ` Josef Bacik [this message]
2020-01-16  6:04 ` [PATCH v6 4/5] btrfs: Reset device size when btrfs_update_device() failed in btrfs_grow_device() Qu Wenruo
2020-01-16  6:04 ` [PATCH v6 5/5] btrfs: volumes: Revert device used bytes when calc_per_profile_avail() failed Qu Wenruo

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