Re: [PATCH v3] iommu/arm-smmu-v3: Shrink command/event/PRI queues in kdump kernel

[Kiryl Shutsemau]

On Wed, Jul 15, 2026 at 12:46:13PM +0100, Kiryl Shutsemau wrote:
> On Mon, Jul 06, 2026 at 09:47:08AM +0100, Kiryl Shutsemau (Meta) wrote:
> > All SMMU queues are sized from the maxima the hardware advertises in IDR1,
> > which can be several megabytes each, and are allocated at probe. The kdump
> > kernel already disables the event and PRI queues (arm_smmu_device_reset()
> > drops CR0_EVTQEN/CR0_PRIQEN) but still allocates them at full size. On
> > systems with many SMMUv3 instances that cost is paid per instance and adds
> > up to tens of megabytes of coherent DMA in the capture kernel.
> > 
> > A kdump capture kernel runs from a small crashkernel reservation and only
> > has to drive the few devices used to save the dump, so deep queues serve
> > no purpose. The queues are not on the DMA data path, so dump throughput is
> > unaffected; a shallower command queue only bounds how many commands may be
> > in flight before a sync, which does not matter for the capture kernel's
> > small device count and modest I/O.
> > 
> > Clamp every queue to a single page when is_kdump_kernel() is true. Doing
> > it in arm_smmu_init_one_queue() covers the command, event and PRI queues
> > in one place. The command queue still holds at least one batch plus a sync
> > (256 entries on a 4K-page kernel, well above CMDQ_BATCH_ENTRIES), so
> > command batching keeps working.
> > 
> > Suggested-by: Kyle McMartin <jkkm@xxxxxxxx>
> > Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
> > Reviewed-by: Breno Leitao <leitao@xxxxxxxxxx>
> > Reviewed-by: Pranjal Shrivastava <praan@xxxxxxxxxx>
> > Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Reviewed-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> > Tested-by: Nicolin Chen <nicolinc@xxxxxxxxxx>
> 
> Gentle ping?

Hey folks,

Can we get the patch applied?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov