[lkml]   [2007]   [Jun]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 4/7][TAKE5] support new modes in fallocate
On Mon, Jun 25, 2007 at 03:46:26PM -0600, Andreas Dilger wrote:
> On Jun 25, 2007 20:33 +0530, Amit K. Arora wrote:
> > I have not implemented FA_FL_FREE_ENOSPC and FA_ZERO_SPACE flags yet, as
> > *suggested* by Andreas in post.
> > If it is decided that these flags are also needed, I will update this
> > patch. Thanks!
> Can you clarify - what is the current behaviour when ENOSPC (or some other
> error) is hit? Does it keep the current fallocate() or does it free it?
> For FA_ZERO_SPACE - I'd think this would (IMHO) be the default - we
> don't want to expose uninitialized disk blocks to userspace. I'm not
> sure if this makes sense at all.

Someone on the XFs list had an interesting request - preallocated
swap files. You can't use unwritten extents for this because
of sys_swapon()s use of bmap() (XFS returns holes for reading
unwritten extents), so we need a method of preallocating that does
not zero or mark the extent unread. i.e. FA_MKSWAP.

I thinkthis would be:

#define FA_FL_NO_ZERO_SPACE 0x08 /* default is to zero space */


That way we can allocate large swap files that don't need zeroing
in a single, fast operation, and hence potentially bring new
swap space online without needed very much memory at all (i.e.
should succeed in most near-OOM conditions).


Dave Chinner
Principal Engineer
SGI Australian Software Group
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2007-06-27 01:31    [W:1.119 / U:2.744 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site