linux-ext4 - Re: [RFC PATCH 0/5] ext4: rework delayed allocated cluster accounting

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Date:   Wed, 16 May 2018 09:00:13 +0800
From:   Liu Bo <obuil.liubo@...il.com>
To:     Eric Whitney <enwlinux@...il.com>
Cc:     linux-ext4@...r.kernel.org, "Theodore Y. Ts'o" <tytso@....edu>
Subject: Re: [RFC PATCH 0/5] ext4: rework delayed allocated cluster accounting

On Mon, May 14, 2018 at 1:56 AM, Eric Whitney <enwlinux@...il.com> wrote:
> The goals of this patch series are to solve the specific bugs
> described in bugzilla #151491 and to arrive at a correct solution
> for delayed allocated cluster accounting for bigalloc file systems
> generally. Under some circumstances, ext4 currently makes gross
> overestimates of the number of reserved clusters required to handle
> bigalloc write requests under delayed allocation.  In addition to
> premature ENOSPC and quota limit failures, these overestimates tend
> to persist over time and in some cases even persist across umounts
> and remounts of an affected file system.
>
> This patch series is a work in progress.  Although it does appear to
> correct all known delayed cluster accounting deficiencies, and
> produces no regressions for all xfstest-bld test cases, it currently
> contains a significant bug that adversely affects ext4's direct I/O
> code.  The next and hopefully final step is to address that bug.
> These patches are being posted now to show the work in progress and
> to solicit comments on its general approach and implementation.
>
> All of the patches in the series must be applied as a unit to obtain
> a correct solution to the problem.  The individual fixes in this
> series have not been submitted separately because they can cause
> new failures or misbehavior to appear.  The effect is to make matters
> even worse for the use case described in bugzilla #151491 until all
> the fixes have been applied together.
>
> This patch series is based on 4.17-rc3.  4.17-rc4 has exhibited a
> number of undiagnosed xfstest-bldtest test failures that appear to be
> unrelated to ext4 and which make comparisons with a regression
> baseline troublesome.  4.17-rc3 is free of those failures.
>

FYI, I'm going thru the whole patch set, the first two patches look good to me.

thanks,
liubo

> Eric Whitney (5):
>   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:  release delayed allocated clusters when removing block ranges
>   ext4: don't release delalloc clusters when invalidating page
>
>  fs/ext4/ext4.h           |  11 +
>  fs/ext4/extents.c        | 661 ++++++++++++++++++++++++++++-------------------
>  fs/ext4/extents_status.c | 303 ++++++++++++++++++++++
>  fs/ext4/extents_status.h |  20 ++
>  fs/ext4/inode.c          | 113 ++++----
>  fs/ext4/mballoc.c        |  11 +-
>  6 files changed, 798 insertions(+), 321 deletions(-)
>
> --
> 2.11.0
>