Thanks Robin for having a look. On Wed, Aug 07, 2024 at 02:13:06PM +0100, Robin Murphy wrote: > On 2024-08-02 7:03 am, Baruch Siach wrote: > > When device DMA limit does not fit in DMA32 zone it should use DMA zone, > > even when DMA zone is stricter than needed. > > > > Same goes for devices that can't allocate from the entire normal zone. > > Limit to DMA32 in that case. > > Per the bot report this only works for CONFIG_ARCH_KEEP_MEMBLOCK, Yeah, I just noticed. > however > the whole concept looks wrong anyway. The logic here is that we're only > forcing a particular zone if there's *no* chance of the higher zone being > usable. For example, ignoring offsets for simplicity, if we have a 40-bit > DMA mask then we *do* want to initially try allocating from ZONE_NORMAL even > if max_pfn is above 40 bits, since we still might get a usable allocation > from between 32 and 40 bits, and if we don't, then we'll fall back to > retrying from the DMA zone(s) anyway. Ah, I did not read the code further down in __dma_direct_alloc_pages(), it does fall back to a GFP_DMA allocation if !dma_coherent_ok(). Similarly with swiotlb_alloc_tlb(), it keeps retrying until the allocation fails. So yes, this patch can be dropped. -- Catalin
