linux-ext4 - Re: [PATCH 0/6] ext4: rework bigalloc reserved cluster accounting

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Date:   Tue, 11 Sep 2018 15:00:16 -0400
From:   Eric Whitney <enwlinux@...il.com>
To:     Eric Whitney <enwlinux@...il.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH 0/6] ext4: rework bigalloc reserved cluster accounting

* Eric Whitney <enwlinux@...il.com>:
> Ext4 can make gross overestimates of the number of reserved clusters
> required to handle bigalloc write requests under delayed allocation,
> resulting in premature ENOSPC and quota limit failures.
> 
> These patches fix the implementation of reserved cluster accounting for
> bigalloc file systems configured to use delayed allocation, and fix the
> specific bugs described in bugzilla #151491.
> 
> These patches also supersede a previous RFC posting from May 2018
> ("ext4: rework delayed allocated cluster accounting"), as well as a more
> recent RFC posting from August 2018 with the same title as this series.
> 
> Eric Whitney (6):
>   ext4: generalize extents status tree search functions
>   ext4: add new pending reservation mechanism
>   ext4: fix reserved cluster accounting at delayed write time
>   ext4: reduce reserved cluster count by number of allocated clusters
>   ext4: adjust reserved cluster count when removing extents
>   ext4: fix reserved cluster accounting at page invalidation time
> 
>  fs/ext4/ext4.h              |  10 +-
>  fs/ext4/ext4_extents.h      |  13 +
>  fs/ext4/extents.c           | 602 ++++++++++++++++++++--------------------
>  fs/ext4/extents_status.c    | 662 ++++++++++++++++++++++++++++++++++++++++++--
>  fs/ext4/extents_status.h    |  84 +++++-
>  fs/ext4/inode.c             | 113 +++++---
>  fs/ext4/mballoc.c           |  14 +-
>  fs/ext4/super.c             |   8 +
>  include/trace/events/ext4.h |  99 +++++--
>  9 files changed, 1207 insertions(+), 398 deletions(-)
> 
> -- 
> 2.11.0
>

An FYI for reviewers -

I've got a v2 for this series in testing.  It fixes some bugs that lead to
infrequent test failures for generic/112 when running the kvm-xfstests
test appliance on the bigalloc and bigalloc_1k test cases.  Basically,
fallocated extents weren't always being handled correctly.  Also,  I've
corrected some misleading nomenclature and a few comments.  These changes
are small and limited to patches 2, 4, and 6 - review effort invested in
v1 should be largely applicable to v2.  The patches look very solid at this
point.

I expect to post v2 tomorrow once a complete test appliance run has
finished.

Thanks,
Eric