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From: Miklos Szeredi <miklos@szeredi.hu>
To: Chengguang Xu <cgxu519@mykernel.net>
Cc: overlayfs <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH] ovl: copy-up optimization for truncate
Date: Mon, 29 Mar 2021 17:13:52 +0200	[thread overview]
Message-ID: <CAJfpeguFdafs65aOgDrJnAh6Tg8bnwP3gP5sUhfsRka5Azctbg@mail.gmail.com> (raw)
In-Reply-To: <20210308111717.2027030-1-cgxu519@mykernel.net>

On Mon, Mar 8, 2021 at 12:17 PM Chengguang Xu <cgxu519@mykernel.net> wrote:
>
> Currently copy-up will copy whole lower file to upper
> regardless of the data range which is needed for further
> operation. This patch avoids unnecessary copy when truncate
> size is smaller than the file size.

This doesn't look right.   If copy up succeeds, resulting in a
truncated file, then we should return success there and then.   Doing
the truncate again and failing (unlikely, but I wouldn't think it
impossible) wouldn't be nice.

But need to be careful, because we could possibly have other attribute
change requests besides ATTR_SIZE, in which case optimizing the
truncate away and returning success wouldn't be correct.

Minor issue: this patch doesn't optimize the truncate to zero case.
That's not a bug, but I'm curious if that is an oversight or
deliberate.

Thanks,
Miklos

  parent reply	other threads:[~2021-03-29 15:14 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-08 11:17 [PATCH] ovl: copy-up optimization for truncate Chengguang Xu
2021-03-08 12:09 ` Amir Goldstein
2021-03-29 15:13 ` Miklos Szeredi [this message]
2021-03-30  7:17   ` Chengguang Xu
2021-04-01 11:15   ` Chengguang Xu
2021-04-01 11:31     ` Miklos Szeredi
2021-04-01 12:39       ` Chengguang Xu

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