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SubjectRe: GFS2 and DLM
On Tue, Jun 27, 2006 at 08:33:39AM +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@elte.hu> wrote:
> > * Christoph Hellwig <hch@infradead.org> wrote:
> >
> > > The code uses GFP_NOFAIL for slab allocator calls. It's been
> > > pointed out here numerous times that this can't work. Andrew, what
> > > about adding a check to slab.c to bail out if someone passes it?
> >
> > reiserfs, jbd and NTFS are all using GFP_NOFAIL ...
> >
> > i dont think this is a huge issue that should block merging.
>
> oh, and XFS has this little gem in its journalling code:
>

[snip misinterpreted code/flag]

> */
> buf = (xfs_caddr_t) kmem_zalloc(NBPP, KM_SLEEP);
> [...]
>
> where kmem_zalloc() may fail!!!

Not with the flags it was given.

> So XFS is apprarently hiding the "journalling allocations must not fail"
> problem by ... crashing? Wow! Most of the other journalling filesystems
> loop on the allocator: the honest ones do it via GFP_NOFAIL, others via
> open-coded infinite retry loops.

No, please look more closely before making such claims.

> sophisticated filesystem, which has many dynamic (and delayed) decisions
> that make the prediction of resource overhead difficult. That's the
> fundamental reason why basically all journalling filesystems either loop
> (or the really enterprise quality ones: crash ;) on allocation failure.

> other problems with the XFS code that are similar in nature to the ones
> you pointed out. (mostly useless wrappers around Linux functionality)

You've missed subtleties in those "useless wrappers", which are
preventing the problem you claim is there.

cheers.

--
Nathan
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