On Wed, Aug 25, 2010 at 09:48:47PM -0400, Ted Ts'o wrote: > On Wed, Aug 25, 2010 at 05:30:42PM -0700, David Rientjes wrote: > > > > We certainly hope that nobody will reimplement the same function without > > the __deprecated warning, especially for order < PAGE_ALLOC_COSTLY_ORDER > > where there's no looping at a higher level. So perhaps the best > > alternative is to implement the same _nofail() functions but do a > > WARN_ON(get_order(size) > PAGE_ALLOC_COSTLY_ORDER) instead? > > Yeah, that sounds better. > > > I think it's really sad that the caller can't know what the upper bounds > > of its memory requirement are ahead of time or at least be able to > > implement a memory freeing function when kmalloc() returns NULL. > > Oh, we can determine an upper bound. You might just not like it. > Actually ext3/ext4 shouldn't be as bad as XFS, which Dave estimated to > be around 400k for a transaction. For a 4k block size filesystem. If I use 64k block size directories (which XFS can even on 4k page size machines), the maximum transaction reservation goes up to at around 3MB, and that's just for blocks being _modified_. It's not the limit on the amount of memory that may need to be allocated during a transaction.... > My guess is that the worst case for > ext3/ext4 is probably around 256k or so; like XFS, most of the time, > it would be a lot less. Right, it usually is a lot less, but one of the big problems is that during low memory situations memory reclaim of the metadata page cache actually causes _more_ memory allocation during tranactions than otherwise would occur....... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
