On 12/15/21 at 07:03am, Hyeonggon Yoo wrote: > 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. Yeah, if it's really <32bit addressing limit on device, it doesn't solve problem. Not sure if devices really has the limitation when kmalloc(GFP_DMA) is invoked kernel driver. > > 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. > > Seems we can do like below. diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 7c7a0b5de2ff..843bc8e5550a 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -4204,7 +4204,8 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...) va_list args; static DEFINE_RATELIMIT_STATE(nopage_rs, 10*HZ, 1); - if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs)) + if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) || + (gfp_mask & __GFP_DMA) && !has_managed_dma()) return; > > > > 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() I grepped and got a list, I will try to start with several easy place, see if we can do something to improve. start with. > > > > 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* Yes, that will be ideal result. This is equivalent to 2), or depends on 2). > > > 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 > > > >> > > > > >> > > > > >> > > > > > > > >
