From: Nikolay Borisov <nborisov@suse.com>
To: Josef Bacik <josef@toxicpanda.com>,
linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] btrfs: force chunk allocation if our global rsv is larger than metadata
Date: Tue, 17 Mar 2020 17:47:21 +0200 [thread overview]
Message-ID: <45abfae5-8795-d0a3-2d4e-5040d1d7e6df@suse.com> (raw)
In-Reply-To: <20200313192848.140759-1-josef@toxicpanda.com>
On 13.03.20 г. 21:28 ч., Josef Bacik wrote:
> Nikolay noticed a bunch of test failures with my global rsv steal
> patches. At first he thought they were introduced by them, but they've
> been failing for a while with 64k nodes.
>
> The problem is with 64k nodes we have a global reserve that calculates
> out to 13mib on a freshly made file system, which only has 8mib of
> metadata space. Because of changes I previously made we no longer
> account for the global reserve in the overcommit logic, which means we
> correctly allow overcommit to happen even though we are already
> overcommitted.
>
> However in some corner cases, for example btrfs/170, we will allocate
> the entire file system up with data chunks before we have enough space
> pressure to allocate a metadata chunk. Then once the fs is full we
> ENOSPC out because we cannot overcommit and the global reserve is taking
> up all of the available space.
>
> The most ideal way to deal with this is to change our space reservation
> stuff to take into account the height of the tree's that we're
> modifying, so that our global reserve calculation does not end up so
> obscenely large.
>
> However that is a huuuuuuge undertaking. Instead fix this by forcing a
> chunk allocation if the global reserve is larger than the total metadata
> space. This gives us essentially the same behavior that happened
> before, we get a chunk allocated and these tests can pass.
>
> This is meant to be a stop-gap measure until we can tackle the "tree
> height only" project.
>
> Fixes: 0096420adb03 ("btrfs: do not account global reserve in can_overcommit")
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Tested-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
next prev parent reply other threads:[~2020-03-17 15:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-13 19:28 [PATCH] btrfs: force chunk allocation if our global rsv is larger than metadata Josef Bacik
2020-03-17 15:47 ` Nikolay Borisov [this message]
2020-04-06 16:00 ` David Sterba
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