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From: Shyam Prasad N <nspmangalore@gmail.com>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: David Howells <dhowells@redhat.com>,
	Steve French <smfrench@gmail.com>,
	linux-ext4@vger.kernel.org
Subject: Re: Regarding ext4 extent allocation strategy
Date: Wed, 14 Jul 2021 06:07:36 +0530	[thread overview]
Message-ID: <CANT5p=pGsU+rgyd-2m+ODOwkxDvdbZKi81DthuuQgzDUXZ9UAQ@mail.gmail.com> (raw)
In-Reply-To: <YO30+XRGAYnME+vy@mit.edu>

On Wed, Jul 14, 2021 at 1:48 AM Theodore Y. Ts'o <tytso@mit.edu> wrote:
>
> On Tue, Jul 13, 2021 at 06:27:37PM +0530, Shyam Prasad N wrote:
> >
> > Also, is this parameter also respected when a hole is punched in the
> > middle of an allocated data extent? i.e. is there still a possibility
> > that a punched hole does not translate to splitting the data extent,
> > even when extent_max_zeroout_kb is set to 0?
>
> Ext4 doesn't ever try to zero blocks as part of a punch operation.
> It's true a file system is allowed to do it, but I would guess most
> wouldn't, since the presumption is that userspace is actually trying
> to free up disk space, and so you would want to release the disk
> blocks in the punch hole case.
>
> The more interesting one is the FALLOC_FL_ZERO_RANGE_FL operation,
> which *should* work by transitioning the extent to be uninitialized,
> but there might be cases where writing a few zero blocks might be
> faster in some cases.  That should use the same code path which
> resepects the max_zeroout configuration parameter for ext4.
>
> Cheers,
>
>                                         - Ted

Thanks a lot for your replies, Ted. This was useful.

-- 
Regards,
Shyam

  reply	other threads:[~2021-07-14  0:37 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13  6:52 Regarding ext4 extent allocation strategy Shyam Prasad N
2021-07-13 11:39 ` Theodore Y. Ts'o
2021-07-13 12:57   ` Shyam Prasad N
2021-07-13 20:18     ` Theodore Y. Ts'o
2021-07-14  0:37       ` Shyam Prasad N [this message]
2022-02-18  3:18   ` Gao Xiang
2022-02-22  2:48     ` Gao Xiang

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