From: Eric Sandeen <sandeen@redhat.com>
Subject: Re: [RFC] Heads up on sys_fallocate()
Date: Tue, 06 Mar 2007 12:23:22 -0600
Message-ID: <45EDB19A.6030103@redhat.com>
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Cc: Ulrich Drepper <drepper@redhat.com>,
	Christoph Hellwig <hch@infradead.org>,
	Mingming Cao <cmm@us.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>, nscott@aconex.com,
	"Amit K. Arora" <aarora@linux.vnet.ibm.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-ext4@vger.kernel.org, suparna@in.ibm.com, alex@clusterfs.com,
	suzuki@in.ibm.com
To: Jan Kara <jack@suse.cz>
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In-Reply-To: <20070306145009.GB3661@duck.suse.cz>
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Jan Kara wrote:
> On Tue 06-03-07 06:36:09, Ulrich Drepper wrote:
>> Christoph Hellwig wrote:
>>> fallocate with the whence argument and flags is already quite complicated,
>>> I'd rather have another call for placement decisions, that would
>>> be called on an fd to do placement decissions for any further allocations
>>> (prealloc, write, etc)
>> Yes, posix_fallocate shouldn't be made more complicated.  But I don't
>> understand why requesting linear layout of the blocks should be an
>> option.  It's always an advantage if the blocks requested this way are
>> linear on disk.  So, the kernel should always do its best to make this
>> happen, without needing an additional option.
>   Actually, it's not that simple. You want linear layout of blocks you are
> going to read. That is not necessary a linear layout of blocks in a single
> file - trace sometime a start of some complicated app like KDE. You find
> it's seeking like a hell because it needs a few blocks from a ton of
> distinct files (shared libs, config files, etc). As these files are mostly
> read only, it's advantageous to interleave them on disk or at least keep
> them close.

At some point shouldn't the apps be fixed, rather than do crazy things
with the filesystem?  :)

-Eric