linux-ext4 - Re: [PATCH] e2fsck: do not allow initialized blocks pass i

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Message-ID: <20180629014513.GC1231@thunk.org>
Date:   Thu, 28 Jun 2018 21:45:13 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] e2fsck: do not allow initialized blocks pass i_size

On Thu, Jun 28, 2018 at 06:07:47PM -0600, Andreas Dilger wrote:
> > But does an RDMA operation actually do a block allocation?  Really?
> > And if it is willing to do a block allocation, why is it not willing
> > to bump i_size?
> 
> It's not that the RDMA does block allocation, but rather that the RDMA
> always transfers and writes the full PAGE_SIZE of data, even if i_size
> is less than the end of the last block.  This simplifies the RDMA code
> so that it can always write the data instead of having to stop at i_size.

Right.  So there are two choices:

1) Keep the blocks beyond i_size marked as uninitialized.  You
transfer and write the full PAGE_SIZE of data, but it simply will
never be available to the user.

2)  Zero the page, write it out to the file, and then extend i_size and
mark the extents as uninitialized.

Why is it that Lustre is choosing to keep i_size where it is, but to
mark the blocks beyond it as initialized?

						- Ted