On Mon 02-03-15 12:33:21, David Rientjes wrote: > On Mon, 2 Mar 2015, Michal Hocko wrote: > > > This basically reverts 47def82672b3 (jbd2: Remove __GFP_NOFAIL from jbd2 > > layer). The deprecation of __GFP_NOFAIL was a bad choice because it led > > to open coding the endless loop around the allocator rather than > > removing the dependency on the non failing allocation. So the > > deprecation was a clear failure and the reality tells us that > > __GFP_NOFAIL is not even close to go away. > > > > It is still true that __GFP_NOFAIL allocations are generally discouraged > > and new uses should be evaluated and an alternative (pre-allocations or > > reservations) should be considered but it doesn't make any sense to lie > > the allocator about the requirements. Allocator can take steps to help > > making a progress if it knows the requirements. > > > > The changelog should state that this only changes the source code, there > is no functional change since alloc_buffer_head() and > kmem_cache_zalloc(transaction_cache) are already implicitly nofail due to > the allocation order. The failure code added by the commit you cite are > never executed. Well, even when those allocation would fail the resulting behavior is basically the same (modulo congestion_wait which imho doesn't make much difference). So I would prefer not getting that way and simply stay with the external loop vs. looping within the allocator. > I agree that if the implementation of the page allocator were to change > with respect to PAGE_ALLOC_COSTLY_ORDER that we'd need __GFP_NOFAIL and > that such an allocation is better handled in the page allocator. > > > Signed-off-by: Michal Hocko <mhocko@xxxxxxx> > > Acked-by: David Rientjes <rientjes@xxxxxxxxxx> Thanks > GFP_NOFS|__GFP_NOFAIL is scary. Yes it is but as I've learned nothing unusual in the fs land and the situation should be improved a lot if we go reservation way suggested by David. Then __GFP_NOFAIL would consume the pre-reserved memory rather than trigger OOM killer. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>