On Wed, Dec 15, 2021 at 04:48:26AM +0000, Hyeonggon Yoo wrote: > > Hello Baoquan and Vlastimil. > > I'm not sure allowing ZONE_DMA32 for kdump kernel is nice way to solve > this problem. Devices that requires ZONE_DMA is rare but we still > support them. > > If we allow ZONE_DMA32 for ZONE_DMA in kdump kernels, > the problem will be hard to find. > Sorry, I sometimes forget validating my english writing :( What I meant: I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA for kdump kernel is nice way to solve this problem. Devices that requires ZONE_DMA memory is rare but we still support them. If we use ZONE_DMA32 memory instead of ZONE_DMA in kdump kernels, It will be hard to the problem when we use devices that can use only ZONE_DMA memory. > What about one of those?: > > 1) Do not call warn_alloc in page allocator if will always fail > to allocate ZONE_DMA pages. > > > 2) let's check all callers of kmalloc with GFP_DMA > if they really need GFP_DMA flag and replace those by DMA API or > just remove GFP_DMA from kmalloc() > > 3) Drop support for allocating DMA memory from slab allocator > (as Christoph Hellwig said) and convert them to use DMA32 (as Christoph Hellwig said) and convert them to use *DMA API* > and see what happens > > Thanks, > Hyeonggon. > > > >> > > >> Maybe the function get_capabilities() want to allocate memory > > >> even if it's not from DMA zone, but other callers will not expect that. > > > > > > Yeah, I have the same guess too for get_capabilities(), not sure about other > > > callers. Or, as ChristophL and ChristophH said(Sorry, not sure if this is > > > the right way to call people when the first name is the same. Correct me if > > > it's wrong), any buffer requested from kmalloc can be used by device driver. > > > Means device enforces getting memory inside addressing limit for those > > > DMA transferring buffer which is usually large, Megabytes level with > > > vmalloc() or alloc_pages(), but doesn't care about this kind of small > > > piece buffer memory allocated with kmalloc()? Just a guess, please tell > > > a counter example if anyone happens to know, it could be easy. > > > > > > > > >> > > >> > kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache( > > >> > kmalloc_info[i].name[KMALLOC_DMA], > > >> > kmalloc_info[i].size, > > >> > -- > > >> > 2.17.2 > > >> > > > >> > > > >> > > > > >
