On Fri 21-07-23 14:20:09, Mike Rapoport wrote: > 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. This would add a very subtle depency of a functionality on the specific boot allocator behavior and that is bad for long term maintenance. -- Michal Hocko SUSE Labs
