linux-ext4 - Re: [RFC] Heads up on sys

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Date:	Sat, 3 Mar 2007 23:45:32 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, suparna@...ibm.com, cmm@...ibm.com,
	alex@...sterfs.com, suzuki@...ibm.com,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [RFC] Heads up on sys_fallocate()

On Friday 02 March 2007 00:38:19 Christoph Hellwig wrote:
> > Forgive me if I haven't put enough thought into it, but would it be
> > useful to create a generic_fallocate() that writes zeroed pages for any
> > non-existent pages in the range?  I don't know how glibc currently
> > implements posix_fallocate(), but maybe the kernel could do it more
> > efficiently, even in generic code.  Maybe we don't care, since the major
> > file systems can probably do something better in their own code.
>
> I'd be more happy to have the write out zeroes loop in glibc.  And
> glibc needs to have it anyway, for older kernels.

A generic_fallocate makes sense to me iff we can do it in the kernel
more significantly more efficiently than in glibc, e.g. by using only
a single page in page cache instead of one for each page to be preallocated.

If  glibc is smart enough to do an optimal implementation, I fully agree
with you.

	Arnd <><
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