linux-ext4 - Re: [PATCH 4/4] ext3: Implement delayed allocation on page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20110502141230.4a7640f9.akpm@linux-foundation.org>
Date:	Mon, 2 May 2011 14:12:30 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/4] ext3: Implement delayed allocation on page_mkwrite
 time

On Mon,  2 May 2011 22:56:56 +0200
Jan Kara <jack@...e.cz> wrote:

> So far, ext3 was allocating necessary blocks for mmapped writes when
> writepage() was called. There are several issues with this. The worst
> being that user is allowed to arbitrarily exceed disk quotas because
> writepage() is called from flusher thread context (which is root) and thus
> quota limits are ignored. Another bad consequence is that data is just lost
> if we find there's no space on the filesystem during ->writepage() time.
> 
> We solve these issues by implementing block reservation in page_mkwrite()
> callback. We don't want to really allocate blocks on page_mkwrite() time
> because for random writes via mmap (as seen for example with applications using
> BerkeleyDB) it results in much more fragmented files and thus much worse
> performance. So we allocate indirect blocks and reserve space for data block in
> page_mkwrite() and do the allocation of data block from writepage().

Yes, instantiating the metadata and accounting the data is a good
approach.  The file layout will be a bit suboptimal, but surely that
will be a minor thing.

But boy, it's a complicated patch!  Are we really sure that we want to
make changes this extensive to our antiquated old fs?  Or do we just
say "yeah, it's broken with quotas - use ext4"?

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html