On Thu, Jun 16, 2016 at 01:26:06PM +0200, Michal Hocko wrote: > @@ -54,6 +54,13 @@ kmem_flags_convert(xfs_km_flags_t flags) > lflags &= ~__GFP_FS; > } > > + /* > + * Default page/slab allocator behavior is to retry for ever > + * for small allocations. We can override this behavior by using > + * __GFP_RETRY_HARD which will tell the allocator to retry as long > + * as it is feasible but rather fail than retry for ever for all > + * request sizes. > + */ > if (flags & KM_MAYFAIL) > lflags |= __GFP_RETRY_HARD; I think this example shows that __GFP_RETRY_HARD is not a good flag because it conflates two seemingly unrelated semantics; the comment doesn't quite make up for that. When the flag is set, - it allows costly orders to invoke the OOM killer and retry - it allows !costly orders to fail While 1. is obvious from the name, 2. is not. Even if we don't want full-on fine-grained naming for every reclaim methodology and retry behavior, those two things just shouldn't be tied together. I don't see us failing !costly order per default anytime soon, and they are common, so adding a __GFP_MAYFAIL to explicitely override that behavior seems like a good idea to me. That would make the XFS callsite here perfectly obvious. And you can still combine it with __GFP_REPEAT. For a generic allocation site like this, __GFP_MAYFAIL | __GFP_REPEAT does the right thing for all orders, and it's self-explanatory: try hard, allow falling back. Whether we want a __GFP_REPEAT or __GFP_TRY_HARD at all is a different topic. In the long term, it might be better to provide best-effort per default and simply annotate MAYFAIL/NORETRY callsites that want to give up earlier. Because as I mentioned at LSFMM, it's much easier to identify callsites that have a convenient fallback than callsites that need to "try harder." Everybody thinks their allocations are oh so important. The former is much more specific and uses obvious criteria. Either way, __GFP_MAYFAIL should be on its own. -- 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>