From: Dave Chinner <david@fromorbit.com>
To: Kaho Ng <ngkaho1234@gmail.com>
Cc: xfs@oss.sgi.com
Subject: Re: [QUESTION] about the freelist allocator in XFS
Date: Tue, 12 Jul 2016 08:53:57 +1000 [thread overview]
Message-ID: <20160711225357.GG1922@dastard> (raw)
In-Reply-To: <CAGeO4WOuQwA7wm_S6352ovDdgiJixn_ztP5=HUVO1d=VmRxfbA@mail.gmail.com>
On Mon, Jul 11, 2016 at 03:06:03PM +0800, Kaho Ng wrote:
> Just wonders why we prefer failing the request of refilling freelist
> with XFS_WANT_CORRUPTED_RETURN(mp, i == 1) in some rare case, rather
> than returning NULLAGBLOCK and allowing the loop in
> xfs_alloc_ag_vextent_size() to try xfs_alloc_ag_vextent_small()...
Have a look at where xfs_alloc_ag_vextent_small() gets the blocks it
returns to the caller if the btree cursor doesn't point to a btree
record we can use. i.e. you can't refill the free list from
xfs_alloc_ag_vextent_small() because it allocates blocks from ...
> In
> such corner case there will always be a lot of small extents at the
> front of the by-count tree, and any truncation changes to the first
> entry in the tree will not result in tree splits and triggering
> assertion failure.
If there are records we can use, then we'll allocate them from the
btree. Failure to allocate from the btree indicates something is
inconsistent, there's a bug in the code or we've got corruption
occuring. A corruption shutdown is the only safe course of action
when we find something confusing like this - if we guess wrong them
we'll only make the bad state/corruption worse.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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next prev parent reply other threads:[~2016-07-11 22:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-07 11:01 [QUESTION] about the freelist allocator in XFS Kaho Ng
2016-07-07 12:13 ` Brian Foster
2016-07-07 22:28 ` Dave Chinner
[not found] ` <CAGeO4WNAdmeXgL4+CAQ1Yqo18XFgv3NZxWVbDTS0xDZLyb3e2w@mail.gmail.com>
2016-07-08 2:29 ` Fwd: " Kaho Ng
[not found] ` <20160708034710.GL12670@dastard>
2016-07-08 4:05 ` Kaho Ng
2016-07-08 5:48 ` Kaho Ng
2016-07-10 23:22 ` Dave Chinner
2016-07-11 7:06 ` Kaho Ng
2016-07-11 22:53 ` Dave Chinner [this message]
2016-07-08 19:17 ` Kaho Ng
2016-07-09 12:26 ` Kaho Ng
2016-07-10 16:57 ` Kaho Ng
2016-07-10 23:27 ` Dave Chinner
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