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 http://lkml.org/lkml/2007/6/14/323 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 */ #define FA_MKSWAP (FA_ALLOCATE | FA_FL_NO_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). Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
