Vlastimil Babka <vbabka@xxxxxxx> writes: > On 25.2.2015 22:24, David Rientjes wrote: >> >>> alloc_pages_preferred_node() variant, change the exact_node() variant to pass >>> __GFP_THISNODE, and audit and adjust all callers accordingly. >>> >> Sounds like that should be done as part of a cleanup after the 4.0 issues >> are addressed. alloc_pages_exact_node() does seem to suggest that we want >> exactly that node, implying __GFP_THISNODE behavior already, so it would >> be good to avoid having this come up again in the future. > > Oh lovely, just found out that there's alloc_pages_node which should be the > preferred-only version, but in fact does not differ from > alloc_pages_exact_node > in any relevant way. I agree we should do some larger cleanup for next > version. > >>> Also, you pass __GFP_NOWARN but that should be covered by GFP_TRANSHUGE >>> already. Of course, nothing guarantees that hugepage == true implies that gfp >>> == GFP_TRANSHUGE... but current in-tree callers conform to that. >>> >> Ah, good point, and it includes __GFP_NORETRY as well which means that >> this patch is busted. It won't try compaction or direct reclaim in the >> page allocator slowpath because of this: >> >> /* >> * GFP_THISNODE (meaning __GFP_THISNODE, __GFP_NORETRY and >> * __GFP_NOWARN set) should not cause reclaim since the subsystem >> * (f.e. slab) using GFP_THISNODE may choose to trigger reclaim >> * using a larger set of nodes after it has established that the >> * allowed per node queues are empty and that nodes are >> * over allocated. >> */ >> if (IS_ENABLED(CONFIG_NUMA) && >> (gfp_mask & GFP_THISNODE) == GFP_THISNODE) >> goto nopage; >> >> Hmm. It would be disappointing to have to pass the nodemask of the exact >> node that we want to allocate from into the page allocator to avoid using >> __GFP_THISNODE. > > Yeah. > >> >> There's a sneaky way around it by just removing __GFP_NORETRY from >> GFP_TRANSHUGE so the condition above fails and since the page allocator >> won't retry for such a high-order allocation, but that probably just >> papers over this stuff too much already. I think what we want to do is > > Alternatively alloc_pages_exact_node() adds __GFP_THISNODE just to > node_zonelist() call and not to __alloc_pages() gfp_mask proper? Unless > __GFP_THISNODE > was given *also* in the incoming gfp_mask, this should give us the right > combination? > But it's also subtle.... > >> cause the slab allocators to not use __GFP_WAIT if they want to avoid >> reclaim. > > Yes, the fewer subtle heuristics we have that include combinations of > flags (*cough* > GFP_TRANSHUGE *cough*), the better. > >> This is probably going to be a much more invasive patch than originally >> thought. > > Right, we might be changing behavior not just for slab allocators, but > also others using such > combination of flags. Any update on this ? Did we reach a conclusion on how to go forward here ? -aneesh -- 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>