On Wed, Jul 19, 2023 at 04:26:04PM -0600, Ross Zwisler wrote: > On Wed, Jul 19, 2023 at 08:44:34AM +0300, Mike Rapoport wrote: > > 3. Switch memblock to use bottom up allocations. Historically memblock > > allocated memory from the top to avoid corrupting the kernel image and to > > avoid exhausting precious ZONE_DMA. I believe we can use bottom-up > > allocations with lower limit of memblock allocations set to 16M. > > > > With the hack below no memblock allocations will end up in ZONE_MOVABLE: > > Yep, I've confirmed that for my use cases at least this does the trick, thank > you! I had thought about moving the memblock allocations, but had no idea it > was (basically) already supported and thought it'd be much riskier than just > adjusting where ZONE_MOVABLE lived. > > Is there a reason for this to not be a real option for users, maybe per a > kernel config knob or something? I'm happy to explore other options in this > thread, but this is doing the trick so far. I think we can make x86 always use bottom up. To do this properly we'd need to set lower limit for memblock allocations to MAX_DMA32_PFN and allow fallback below it so that early allocations won't eat memory from ZONE_DMA32. Aside from x86 boot being fragile in general I don't see why this wouldn't work. -- Sincerely yours, Mike.
